msm: vidc: Fix an issue with queueing of already mapped buffer

Driver was holding a buffer whose ref count was 1. Since firmware had
already released the reference of this buffer, there was no need for
driver to hold it. By holding the buffer in driver, the buffer gets
lost and is not returned back to client after a flush is issued.
Fix this issue by holding the buffer in driver only if firmware is holding
a reference of the mapped buffer, i.e, the ref count of the buffer is 2.

Change-Id: I18f1de06eee72019f340f68407c07ec76f1539d1
Signed-off-by: Arun Menon <avmenon@codeaurora.org>