[SPARC]: Missing #include <linux/mm.h> in drivers/sbus/char/flash.c

drivers/sbus/char/flash.c does use macros VM_READ and such, needs to include
linux/mm.h.

Signed-off-by: Horst H. von Brand <vonbrand@inf.utfsm.cl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>