Include linux/sched.h in arch/arm/mm/fault.c

When building with !MMU, task_struct is not defined. Just include the
relevant file.
Signed-off-by: NCatalin Marinas <catalin.marinas@arm.com>

arch/arm/mm/fault.c

@@ -16,6 +16,7 @@
 #include <linux/kprobes.h>
 #include <linux/uaccess.h>
 #include <linux/page-flags.h>
+#include <linux/sched.h>
 
 #include <asm/system.h>
 #include <asm/pgtable.h>