msm: kgsl: don't use sscanf()

sscanf() is really hard to get right with different variable types
and it shouldn't be used when kstrtoul works just as well (and is
way safer).

Change-Id: Ic0dedbad56af5bbee4fc833701d8bc93b118efa9
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>