drm: Flatten drm_mode_connector_list_update() a bit

Use 'continue' to eliminate one indent level from
drm_mode_connector_list_update(). And while at it,
make 'found_it' bool.

Cc: Adam Jackson <ajax@redhat.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1449177255-9515-5-git-send-email-ville.syrjala@linux.intel.com