clk: mdss: fix bugs when parsing mdss regulators

There are two definitions of struct dss_vreg in mdss driver.
One is used during parsing regulators from device tree file,
the other is used when operating regulators. This introduces
different understanding of dss_vreg data in these two places.
Future plan is to have only one definition for these shared
data structure. Currently only make dss_vreg in sync to fix
this issue.

CRs-Fixed: 2054371
Change-Id: I4f16e1409c832432fa1df73b0ae030176b664e58
Signed-off-by: Ray Zhang <rayz@codeaurora.org>