msm: mdss: avoid flagging error for retire fence fd

For cases such as the rotator interface, flags to
indicate retire fence file descriptors are not set.
Do not return error while copying these file descriptors
for such interfaces. This avoids the driver from setting
false positive error flags to user space processes in
usecases where retire fence fd is not present.

CRs-Fixed: 663793
Change-Id: I7918520764c364ee11f469ea757c38ef46bf93cd
Signed-off-by: Manoj Rao <manojraj@codeaurora.org>