msm: mdss: fix software reset logic hw programming

While refactoring VBIF registers programming
(commit 41efd125)
software reset programming was switched from using
mdp based to vbif base, this is incorrect programming
and software reset wouldn't work in case hardware
behaves incorrectly.

Change-Id: I8738bc4fc96ec8ba7130a891231c34bd4ce10449
Signed-off-by: Adrian Salido-Moreno <adrianm@codeaurora.org>