msm: kgsl: Update TTBR0 when switching non current ringbuffer

When switching context on non current ringbuffer we are currently
only updating the pagetable name. Update TTBR0 also so that when
we preempt back to this ringbuffer we use the correct pagetable.

Change-Id: Ifc631de92e48d25e065a6bc12671811bfdadc635
Signed-off-by: Tarun Karra <tkarra@codeaurora.org>