[MIPS] Fix value of O_TRUNC

A "cleanup" almost two years ago deleted the old definition from
<asm/fcntl.h>, so asm-generic/fcntl.h defaulted it to the the same
value as FASYNC ...   which happened to be the wrong thing.
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

include/asm-mips/fcntl.h

@@ -13,6 +13,7 @@
 #define O_SYNC		0x0010
 #define O_NONBLOCK	0x0080
 #define O_CREAT         0x0100	/* not fcntl */
+#define O_TRUNC		0x0200	/* not fcntl */
 #define O_EXCL		0x0400	/* not fcntl */
 #define O_NOCTTY	0x0800	/* not fcntl */
 #define FASYNC		0x1000	/* fcntl, for BSD compatibility */