msm: kgsl: Compare pid pointer instead of TGID for a new process

BugLink: https://bugs.launchpad.net/bugs/1931727



There is a possibility of sharing process_private between two unrelated
processes due to PID wrapping. In kgsl_process_private_new(), instead
of checking numeric TGID, compare the unique pid pointer of the current
process with that of the existing processes in kgsl process list to
allow sharing of process_private data judiciously. Also, in all required
functions get TGID/PID of a process from its struct pid.

Change-Id: I0e3d5d79275cdb3f3c304fb36322ad56b0d0b227
Signed-off-by: Archana Sriram <apsrir@codeaurora.org>
Signed-off-by: Amit Kushwaha <kushwaha@codeaurora.org>
(cherry picked from commit f6b06c87de4b1b31451382eac3a5c68ac806fa82)
Signed-off-by: Shrirang Bagul <shrirang.bagul@canonical.com>