msm: kgsl: Ensure _free_pt() gets called on error case

During the global pt initialization there is possibility that
we set invalid token in iommu_fault_handler on error of
smmu aperture programming. Fix this to handle the error
gracefully to avoid incorrect pointer dereferences.

Change-Id: Ib1c24c1d078c68fd86de9f19cbb72bf7b2b57f21
Signed-off-by: Hareesh Gundu <hareeshg@codeaurora.org>