[media] mt2063: properly handle return error codes

Fix a series of warnings when compiled with W=1:

drivers/media/tuners/mt2063.c: In function 'mt2063_setreg':
drivers/media/tuners/mt2063.c:290:2: warning: comparison of unsigned expression < 0 is always false [-Wtype-limits]
...
drivers/media/tuners/mt2063.c:2013:2: warning: comparison of unsigned expression < 0 is always false [-Wtype-limits]

drivers/media/tuners/mt2063.c:2271:14: warning: no previous prototype for 'tuner_MT2063_SoftwareShutdown' [-Wmissing-prototypes]
drivers/media/tuners/mt2063.c:2286:14: warning: no previous prototype for 'tuner_MT2063_ClearPowerMaskBits' [-Wmissing-prototypes]

Several of those warnings are real bugs: the error status code
used to be unsigned, but they're assigned to negative error
codes.

Fix it by using unsigned int.

While here, comment the two power management functions, while we
don't add a code there to properly handle tuner suspend/resume.

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