arm-smmu: In smmu shutdown path return early for kgslsmmu

KGSL requested for arm_smmu_flush_iotlb_all which enables
GPU SMMU CLOCK and same time smmu shutdown is called which
disables same clock and latter in tlbi path accessing register
GPU_GFX_SMMU_CBn_TLBIASID causing NOC. So do not disable the
clock in shutdown path.

Change-Id: I2a0660b476690d632ba812d893a3522899f1973d
Signed-off-by: Swetha Chikkaboraiah <quic_schikk@quicinc.com>
Signed-off-by: Deepak Suresh <quic_deesur@quicinc.com>