[media] cx25821: fix sparse warnings

drivers/media/pci/cx25821/cx25821-cards.c:49:20: warning: symbol 'cx25821_bcount' was not declared. Should it be static?
drivers/media/pci/cx25821/cx25821-video-upstream.c:162:33: warning: incorrect type in assignment (different base types)
drivers/media/pci/cx25821/cx25821-video-upstream.c:163:33: warning: incorrect type in assignment (different base types)
drivers/media/pci/cx25821/cx25821-video-upstream.c:164:33: warning: incorrect type in assignment (different base types)
drivers/media/pci/cx25821/cx25821-video-upstream.c:165:33: warning: incorrect type in assignment (different base types)
drivers/media/pci/cx25821/cx25821-medusa-video.h:43:16: warning: symbol '_num_decoders' was not declared. Should it be static?
drivers/media/pci/cx25821/cx25821-medusa-video.h:44:16: warning: symbol '_num_cameras' was not declared. Should it be static?
drivers/media/pci/cx25821/cx25821-medusa-video.h:46:14: warning: symbol '_video_standard' was not declared. Should it be static?
drivers/media/pci/cx25821/cx25821-medusa-video.h:47:5: warning: symbol '_display_field_cnt' was not declared. Should it be static?
After analyzing the last four warnings carefully it became clear that these
variables were really completely unused. As a result of that the call to
medusa_set_decoderduration() is now dubious since the duration is always 0.
Without documentation, however, I can't tell what the right value is.

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