iommu/omap: Remove iopgtable_clear_entry_all() from driver remove

The function iopgtable_clear_entry_all() is used for clearing all
the page table entries. These entries are neither created nor
initialized during the OMAP IOMMU driver probe, and are managed
only when a client device attaches to the IOMMU. So, there is no
need to invoke this function on a driver remove.

Removing this fixes a NULL pointer dereference crash if the IOMMU
device is unbound from the driver with no client device attached
to the IOMMU device.

Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>