fs/ramfs/ extern cleanup

- internal.h shouldn't duplicate the extern declaration for
  ramfs_file_operations already in include/linux/ramfs.h
- file-mmu.c needs two #include's for seeing the extern declarations
  of it's global struct's

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>