msm: mdss: reset the skip buffer flag to avoid memory leak

Pan display path can call buffer alloc and use one of the
buffer. It will enable the skip detach enabled for that
buffer. This buffer moves to free queue when atomic api
stage next set of layers. It can lead to memory leak when
atomic API path reuse the same buffer without resetting
the detach flag. Ideally, it should be reset for each
attach call.

Change-Id: I96e2c030669539d8e5dc7205abc233ecc7118bdb
Signed-off-by: Dhaval Patel <pdhaval@codeaurora.org>