In preparation for marking file_operations as const.

Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Acked-by: NArjan van de Ven <arjan@infradead.org>
Signed-off-by: NStephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NPaul Mackerras <paulus@samba.org>