drm/msm/dsi-staging: handle reset gpio parsing error properly

Currently in dsi driver any failure while parsing panel
reset gpio during probe is not handled gracefully, which
causes system boot up issues. Fix this issue by properly
propagating the error number to caller function.

Change-Id: I49225dad2edf7f09e8dca0fe009a59c013835ba5
Signed-off-by: Sandeep Panda <spanda@codeaurora.org>