msm: kgsl: don't use sscanf()

Friends do not let friends use sscanf().

CRs-Fixed: 563605
Change-Id: Ic0dedbad56af5bbee4fc833701d8bc93b118efa9
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>
Signed-off-by: Ananta Kishore K <akollipa@codeaurora.org>
cpufreq: Bring back cpu voltage interface