Revert "msm: kgsl: Call dma_buf_unmap_attachment() early"

This reverts commit 0e47811b.

This patch is reported to be causing screen corruption issues
with video use cases, so reverting this change.

Change-Id: I556dd1a6ede9261db102985eea55b8ffc91cde37
Signed-off-by: Pankaj Gupta <quic_gpankaj@quicinc.com>