[media] tuner-core: Some cleanups at check_mode/set_mode
[media] tuner-core: Some cleanups at check_mode/set_mode

Properly document those functions and do some cleanups around that.
There's just one behavior change on this patchset: it will now restore
TV frequency when changing from radio to TV mode.

Signed-off-by: Mauro Carvalho Chehab <ad86ba2154032c9f55743a190faa2459a9d61d42@redhat.com>

KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs