drm/msm/sde: avoid encoder-connector checks with cont-splash

When continuous splash is enabled, connector states
are not properly updated with the encoder associated
with it. This is by design, so avoid all making
such request there by avoiding unnecessary errors
during the bootup.

Change-Id: Id34938aa658fa19339ddf98a81d03025795ad6ab
Signed-off-by: Samantha Tran <samtran@codeaurora.org>