iommu: clean up includes

The file mach/msm_bus.h should not be included,
instead the file linux/msm-bus.h should be.
Also remove an unneeded include.

Change-Id: I6e060739977f8604409f660c72c9a983eaddfa45
Signed-off-by: Larry Bassel <lbassel@codeaurora.org>