disp: msm: sde: increment refcount of dma_fence before access

Add changes to increment refcount of dma_fence before accessing
the input_fence structure in plane_state through debug_fs node and
decrement once access is finished. This prevents the use after free
issues when accessed through debug_fs node.

Change-Id: I262336ce2b86a94d7662d834e8fd3509dadda1bd
Signed-off-by: Jayaprakash <jmadiset@codeaurora.org>