fbdev: msm: Handle rotator init failure correctly

In case 'mdss_rotator_req_init' function fails, the
error handling code frees the 'req' struct which
is not yet allocated. Correct this error scenario
by freeing the 'req' struct only for cases where it
is already allocated.

Change-Id: If9089c59497fef628528e6a462eb5a4699453214
Signed-off-by: Nirmal Abraham <nabrah@codeaurora.org>