xen/arm: smmuv1: Revert associating the group pointer with the S2CR

xen/arm: smmuv1: Revert associating the group pointer with the S2CR

Revert the code that associates the group pointer with the S2CR as this
code causing an issue when the SMMU device has more than one master
device with same stream-id. This issue is introduced by commit
0435784cc75d ("xen/arm: smmuv1: Intelligent SMR allocation”

Reverting the code will not impact to use of SMMU if two devices use the
same stream-id but each device will be in a separate group. This is the same
behaviour before the code is merged.

Fixes: 0435784cc75d ("xen/arm: smmuv1: Intelligent SMR allocation”
Signed-off-by: Rahul Singh <rahul.singh@arm.com>