sh: arch/sh/kernel/process_32.c needs linux/prefetch.h.

Trivial build fix for certain configurations that don't grab
linux/prefetch.h via alternate means (specifically SH-2 and SH-3 parts).
Signed-off-by: Paul Mundt <lethal@linux-sh.org>

arch/sh/kernel/process_32.c

@@ -21,6 +21,7 @@
 #include <linux/fs.h>
 #include <linux/ftrace.h>
 #include <linux/hw_breakpoint.h>
+#include <linux/prefetch.h>
 #include <asm/uaccess.h>
 #include <asm/mmu_context.h>
 #include <asm/system.h>