drm/sde: don't return error when fail to set panel pin ctrl

Panel pin control is not mandatory for all of the DSI panels.
If the panel is using bridge chips, such as ADV7533, it doesn't
have to configure the panel pin controls.

Change-Id: I48d862a9c67d52c0ed8c3c0309b0ff56d13e97f4
Signed-off-by: Jin Li <jinl@codeaurora.org>
Signed-off-by: Yunyun Cao <yunyunc@codeaurora.org>