[media] cx25821: fix compiler warnings

media_build/v4l/cx25821-core.c: In function 'cx_i2c_read_print':
media_build/v4l/cx25821-core.c:386:6: warning: variable 'value' set but not used [-Wunused-but-set-variable]
media_build/v4l/cx25821-core.c: In function 'cx25821_dev_setup':
media_build/v4l/cx25821-core.c:899:6: warning: variable 'io_size' set but not used [-Wunused-but-set-variable]
media_build/v4l/cx25821-core.c: In function 'cx25821_irq':
media_build/v4l/cx25821-core.c:1321:18: warning: variable 'pci_mask' set but not used [-Wunused-but-set-variable]
media_build/v4l/cx25821-i2c.c: In function 'cx25821_i2c_read':
media_build/v4l/cx25821-i2c.c:365:6: warning: variable 'retval' set but not used [-Wunused-but-set-variable]
media_build/v4l/cx25821-medusa-video.c: In function 'medusa_enable_bluefield_output':
media_build/v4l/cx25821-medusa-video.c:39:6: warning: variable 'ret_val' set but not used [-Wunused-but-set-variable]
media_build/v4l/cx25821-medusa-video.c: In function 'medusa_set_resolution':
media_build/v4l/cx25821-medusa-video.c:435:6: warning: variable 'ret_val' set but not used [-Wunused-but-set-variable]
media_build/v4l/cx25821-medusa-video.c: In function 'medusa_set_decoderduration':
media_build/v4l/cx25821-medusa-video.c:498:6: warning: variable 'ret_val' set but not used [-Wunused-but-set-variable]
media_build/v4l/cx25821-video.c: In function 'cx25821_dump_video_queue':
media_build/v4l/cx25821-video.c:116:25: warning: variable 'buf' set but not used [-Wunused-but-set-variable]
media_build/v4l/cx25821-video.c: In function 'cx25821_buffer_prepare':
media_build/v4l/cx25821-video.c:561:20: warning: variable 'line1_offset' set but not used [-Wunused-but-set-variable]
media_build/v4l/cx25821-video.c: In function 'video_ioctl_set':
media_build/v4l/cx25821-video.c:1834:6: warning: variable 'value' set but not used [-Wunused-but-set-variable]
media_build/v4l/cx25821-video-upstream.c: In function 'cx25821_upstream_irq':
media_build/v4l/cx25821-video-upstream.c:641:6: warning: variable 'msk_stat' set but not used [-Wunused-but-set-variable]
media_build/v4l/cx25821-video-upstream-ch2.c: In function 'cx25821_upstream_irq_ch2':
media_build/v4l/cx25821-video-upstream-ch2.c:591:6: warning: variable 'msk_stat' set but not used [-Wunused-but-set-variable]
media_build/v4l/cx25821-audio-upstream.c: In function 'cx25821_upstream_irq_audio':
media_build/v4l/cx25821-audio-upstream.c:589:6: warning: variable 'msk_stat' set but not used [-Wunused-but-set-variable]

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>