drm/vc4: Delete unnecessary checks before two function calls

The following functions test whether their argument is NULL
and then return immediately.
* drm_fbdev_cma_hotplug_event
* drm_fbdev_cma_restore_mode

Thus the tests around their calls are not needed.

This issue was detected by using the Coccinelle software.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/fb33d930-6a5c-c501-6676-26bd486f1cb5@users.sourceforge.net