arm: mach-msm: fix error handling in msm_iommu_probe()

msm_iommu_probe() didn't free mem_region and mapped IO.
Also if request_mem_region() failed then error handling
code dereferenced NULL pointer.

Signed-off-by: Vasiliy Kulikov <segooon@gmail.com>
Acked-by: Stepan Moskovchenko <stepanm@codeaurora.org>
Signed-off-by: Daniel Walker <dwalker@codeaurora.org>