[media] wl128x: fix fmdbg compiler warning

fmdrv_common.c: In function 'fm_download_firmware':
fmdrv_common.c:1259:2: warning: format '%d' expects argument of type 'int', but argument 3 has type 'size_t' [-Wformat=]
   fmdbg("Firmware(%s) length : %d bytes\n", fw_name, fw_entry->size);
   ^

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