drivers/iommu/msm_iommu_dev.c: fix leak and clean up error paths

Fix two obvious problems:

1. We have registered msm_iommu_driver first, and need unregister it
   when registered msm_iommu_ctx_driver fail

2. We don't need to kfree drvdata before kzalloc was successful.

[akpm@linux-foundation.org: remove now-unneeded initialization of ctx_drvdata, remove unneeded braces]
Signed-off-by: Libo Chen <libo.chen@huawei.com>
Acked-by: David Brown <davidb@codeaurora.org>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: James Hogan <james.hogan@imgtec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>