msm: kgsl: Remove unnecessary NULL checks

Currently there are a few unnecessary NULL checks for pointers to
kgsl_drawobj_sync_event. The pointers will always be valid at
these points and are moreover already accessed in the same functions
prior to the NULL checks. Hence remove the unnecessary NULL checks.

Change-Id: I65197ea8ad4df7b28445a95165bf4b57f735a6d8
Signed-off-by: Puranam V G Tejaswi <quic_pvgtejas@quicinc.com>