drm: Simplify and defend later checks when disabling a crtc
drm: Simplify and defend later checks when disabling a crtc

By setting the FB of a CRTC to NULL, we are turning off the CRTC (and so
disable the unused encoders and connectors). As such we can simplify the
later tests by making sure the set->mode is NULL. Setting the
num_connectors to zero means that we do not need to loop over the unused
connectors.

All current usage appears correct, this only builds additional defense
into the routine.

References: https://bugzilla.kernel.org/show_bug.cgi?id=27722
Tested-by: Takashi Iwai <4596b3305151c7ee743192a95d394341e3d3b644@suse.de>
Signed-off-by: Chris Wilson <711c73f64afdce07b7e38039a96d2224209e9a6c@chris-wilson.co.uk>

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