[media] v4l: fix compiler warnings

[media] v4l: fix compiler warnings

media_build/v4l/au0828-video.c: In function 'au0828_irq_callback':
media_build/v4l/au0828-video.c:123:6: warning: variable 'rc' set but not used [-Wunused-but-set-variable]
media_build/v4l/cx23888-ir.c: In function 'pulse_clocks_to_clock_divider':
media_build/v4l/cx23888-ir.c:334:6: warning: variable 'rem' set but not used [-Wunused-but-set-variable]
media_build/v4l/cx25840-ir.c: In function 'pulse_clocks_to_clock_divider':
media_build/v4l/cx25840-ir.c:319:6: warning: variable 'rem' set but not used [-Wunused-but-set-variable]
media_build/v4l/cx25840-ir.c: In function 'cx25840_ir_tx_write':
media_build/v4l/cx25840-ir.c:863:21: warning: variable 'c' set but not used [-Wunused-but-set-variable]
media_build/v4l/em28xx-audio.c: In function 'snd_em28xx_hw_capture_params':
media_build/v4l/em28xx-audio.c:346:31: warning: variable 'format' set but not used [-Wunused-but-set-variable]
media_build/v4l/em28xx-audio.c:346:25: warning: variable 'rate' set but not used [-Wunused-but-set-variable]
media_build/v4l/em28xx-audio.c:346:15: warning: variable 'channels' set but not used [-Wunused-but-set-variable]
media_build/v4l/hdpvr-control.c: In function 'get_input_lines_info':
media_build/v4l/hdpvr-control.c:98:6: warning: variable 'ret' set but not used [-Wunused-but-set-variable]
media_build/v4l/hdpvr-video.c: In function 'hdpvr_try_ctrl':
media_build/v4l/hdpvr-video.c:955:6: warning: variable 'ret' set but not used [-Wunused-but-set-variable]
media_build/v4l/saa7134-video.c: In function 'saa7134_s_tuner':
media_build/v4l/saa7134-video.c:2030:6: warning: variable 'rx' set but not used [-Wunused-but-set-variable]
media_build/v4l/sn9c102_core.c: In function 'sn9c102_stream_interrupt':
media_build/v4l/sn9c102_core.c:998:7: warning: variable 'timeout' set but not used [-Wunused-but-set-variable]

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Janne Grunau <j@jannau.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>