drm/msm/sde: avoid sde ctx unbalanced call in fence create failure

Fence create may fail while looking for unused fd or
during sync_file creation process. That leads to
dma_fence_put API called followed by fence->release() call.
The fence release API decrements the sde_ctx refcount
and it may lead to free the context unexpectedly.
This patch acquires the sde_ctx refcount before unused
fd and syn_file creation calls and balances the call
during failure case.

Change-Id: I56069a3b5472a4d80e0f451247b3ec6167bc91a6
Signed-off-by: Lakshmi Narayana Kalavala <lkalaval@codeaurora.org>