msm: kgsl: Add check not to decrement refcount when debug_fs is disabled

As there is no increment in ref_count on context when debug_fs is
disabled, ensure there is no decrement in ref_count either.

Change-Id: I8da258a78a8b82ee967b1c944209f6777439e682
Signed-off-by: Prakruthi Deepak Heragu <pheragu@codeaurora.org>