fat.c: Add missing include

This file references rtc functions and implicitly includes <rtc.h>
today. Add this explicitly.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/fs/fat/fat.c b/fs/fat/fat.c
index e2570e8..89f2acb 100644
--- a/fs/fat/fat.c
+++ b/fs/fat/fat.c
@@ -21,6 +21,7 @@
 #include <part.h>
 #include <malloc.h>
 #include <memalign.h>
+#include <rtc.h>
 #include <asm/cache.h>
 #include <linux/compiler.h>
 #include <linux/ctype.h>