ARM: dts: msm: rename the display gpio regulator for qrd855

Other module could use the same name gpio-regulator as the
display used, that will be confused and will override the
config.

Change-Id: I286993a4abc4f60484dbd5aad534fa50c0c3094e
Signed-off-by: Yuan Zhao <yzhao@codeaurora.org>