msm: kgsl: Fix permission in /sys/kernel/gpu/

Set read permission for sysfs nodes in /sys/kernel/gpu/ to read the
value appropriately.

CRs-Fixed: 2765368
Change-Id: Iba74b783c47e5a3bd0c0546cb5103f5fb705f74b
Signed-off-by: Young Hwan Kwak <ykwak@codeaurora.org>