msm: kgsl: Fix reading lm_sequence in _execute_reg_sequence()

Added proper checks while reading lm_sequence array so that it
is not accessed beyond lm_size.

CRs-Fixed: 2175951
Change-Id: I639b07fba275aad0f62cc03fa11201c126e24812
Signed-off-by: Archana Sriram <apsrir@codeaurora.org>