V4L/DVB: cx88: Fix some gcc warnings

drivers/media/video/cx88/cx88-dsp.c: In function ‘detect_a2_a2m_eiaj’:
drivers/media/video/cx88/cx88-dsp.c:158: warning: ‘carrier_freq’ may be used uninitialized in this function
drivers/media/video/cx88/cx88-dsp.c:158: warning: ‘stereo_freq’ may be used uninitialized in this function
drivers/media/video/cx88/cx88-dsp.c:158: warning: ‘dual_freq’ may be used uninitialized in this function

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>