msm: camera: core: Delete request from pending list in case of error

While preparing hw for request, there is a possiblity of receiving
invalid sync object. In this case, we need to return error. By this
time, the request is already in pending list. While returning error,
request is moved back to free list. But deleting from the pending list
was missed.
This commit deleted the request from the pending list if the sync object
received is invalid.

CRs-Fixed: 2660625
Change-Id: Id619452889476b0c2811c8560361205b0d89bcb9
Signed-off-by: Gaurav Jindal <gjindal@codeaurora.org>