iommu/omap: Remove redundant clock handling on ISR

For the interrupt to be generated, the mmu clock should be already
enabled while translating a virtual address, so, this call to clock
handling is just increasing/decreasing the counter.

This works now, because its users need the same clock and they
indirectly power the mmu, in this interrupt context the handling of
clocks inside the ISR doesn't seem to be needed nor helping.

Next patch should also correct the dependency on clients to handle
iommu clocks.

Signed-off-by: Omar Ramirez Luna <omar.luna@linaro.org>
Tested-by: Ohad Ben-Cohen <ohad@wizery.com>
Signed-off-by: Joerg Roedel <joro@8bytes.org>