Remove redundant check for CONFIG_MMU

The checks for CONFIG_MMU at this location are duplicated as all the code is
located inside a #ifndef CONFIG_MMU block. So the first conditional block will
always be included while the second never will.

Signed-off-by: Christoph Egger <siccegge@stud.informatik.uni-erlangen.de>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>