msm: kgsl: Fix calculation of size in _load_regfile

During firmware load, there could be data over reads
due to calculation of lm_size and lm_sequence from
block and block_size. Added bounds checking to prevent
this and improved the size calculation.

CRs-Fixed: 2107981
Change-Id: Ib4283951b0d6c8fb699af1f85e657981ad4c0318
Signed-off-by: Archana Sriram <apsrir@codeaurora.org>