Define _STATFS_F_FRSIZE for MIPS

After discussion on the busybox mailinglist.

Reported-by: Ralf Friedl <Ralf.Friedl@online.de>
Signed-off-by: Waldemar Brodkorb <wbx@uclibc-ng.org>

libc/sysdeps/linux/mips/bits/statfs.h

@@ -69,3 +69,4 @@ struct statfs64
 
 /* Tell code we have these members.  */
 #define _STATFS_F_NAMELEN
+#define _STATFS_F_FRSIZE