drm/msm/sde: fix to update controller in all phys encoders

In some cases (i.e. dual-dsi scenarios) driver can have
two physical interfaces with one single controller.
For those cases, make sure that driver populates both
physical encoders with the pointer to the controller
hardware for the continuous splash case.

Change-Id: I0edea2048b6790221f9015da786eaa3d0573d0e8
Signed-off-by: Ingrid Gallardo <ingridg@codeaurora.org>