msm: kgsl: Fix attributes of read only files

Preempt_count is a read only file. So remove the
write permissions from its attributes.

Change-Id: I8327624e8b09d9968be26197f6c25f2dcc373822
Signed-off-by: Harshdeep Dhatt <hdhatt@codeaurora.org>
Signed-off-by: Urvashi Agrawal <urvaagra@codeaurora.org>