Fix typo in fs.h

fs.h defined _FH_H_ rather than _FS_H_

Change-Id: I710ef53e88d3601e486fde9957f6d022871d9602
Signed-off-by: Markus Mayer <code@mmayer.net>
diff --git a/fastboot/fs.h b/fastboot/fs.h
index 8388629..8444081 100644
--- a/fastboot/fs.h
+++ b/fastboot/fs.h
@@ -1,5 +1,5 @@
 #ifndef _FS_H_
-#define _FH_H_
+#define _FS_H_
 
 #include <stdint.h>