drm/msm/sde: add parentheses for inline kickoff

Add explicit parentheses around the if statement and loop
for the sde_plane_kickoff function call. This is needed
to avoid a compiler warning for newer versions of gcc.

Change-Id: I299d0926f2fb5b0187a2447abb6262bbb3fcffc1
Signed-off-by: Clarence Ip <cip@codeaurora.org>