sh/mm/pg-sh7705.c must #include <linux/fs.h>

This patch fixes the following compile error:

<--  snip  -->

...
  CC      arch/sh/mm/pg-sh7705.o
/home/bunk/linux/kernel-2.6/git/linux-2.6/arch/sh/mm/pg-sh7705.c: In function 'ptep_get_and_clear':
/home/bunk/linux/kernel-2.6/git/linux-2.6/arch/sh/mm/pg-sh7705.c:130: error: implicit declaration of function 'mapping_writably_mapped'
make[2]: *** [arch/sh/mm/pg-sh7705.o] Error 1

<--  snip  -->

Signed-off-by: Adrian Bunk <adrian.bunk@movial.fi>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>