fs/9p: translate O_TRUNC into OTRUNC

This one hits both 9P2000 and .u as it appears v9fs has never translated
the O_TRUNC flag.
Signed-off-by: Joakim Sindholt <opensource@zhasha.com>
Signed-off-by: Eric Van Hensbergen <ericvh@kernel.org>

fs/9p/vfs_inode.c

@@ -178,6 +178,9 @@ int v9fs_uflags2omode(int uflags, int extended)
 		break;
 	}
 
+	if (uflags & O_TRUNC)
+		ret |= P9_OTRUNC;
+
 	if (extended) {
 		if (uflags & O_EXCL)
 			ret |= P9_OEXCL;