msm: kgsl: Set FSR to 0 on IOMMU pagefault

On IOMMU pagefault the FSR is not cleared until the IOMMU
is reset and re-attached to the GPU device. Until FSR clears
the system will keep generating fault interrupts. Clear the
FSR when iommu is stopped in kgsl driver to prevent system
from generating additional fault interrupts for the same
fault until the IOMMU is re-attached