arm/omap: use generic_file_llseek in iommu_debug

In future kernels, debugfs files need to specify
the llseek operation explicitly to allow seeking.
This sets the llseek operation in the omap iommu
debugfs files to generic_file_llseek, which is
appropriate for files using simple_read_from_buffer.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Tony Lindgren <tony@atomide.com>
Cc: linux-omap@vger.kernel.org