msm: kgsl: Fix out of bound access in the simple_read_from_buffer()

If strlen() is used to find the size of buffer, there is a possibility
that size can go up to INT_MAX, if buffer is not NULL terminated.
To avoid this, pass size directly to simple_read_from_buffer().

Change-Id: Id3e3fc53279e9be20b2a5cddea0a5560f776be62
Signed-off-by: Sravankumar bijili <csbijil@codeaurora.org>