msm: sde: simulate timestamp on skipped inline interrupt

If an interrupt for regdma completion is missed for any reason,
the ISR needs to indicate that more than one rotation request
has been completed. This patch updates the software timestamp
simulation for inline rotations to select a timestamp matching
the current incoming interrupt, instead of simply selecting
the timestamp of the oldest request.

CRs-Fixed: 2062038
Change-Id: I4c651f277f4ae0eeb4d26a80feb5912c5ed56e17
Signed-off-by: Clarence Ip <cip@codeaurora.org>