mtd: disable trx_check() for ar71xx, fixes a regression introduced in r42403

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

SVN-Revision: 42405

package/system/mtd/src/trx.c

@@ -101,6 +101,7 @@ err:
 	return -1;
 }
 
+#ifndef target_ar71xx
 int
 trx_check(int imagefd, const char *mtd, char *buf, int *len)
 {
@@ -141,6 +142,7 @@ trx_check(int imagefd, const char *mtd, char *buf, int *len)
 	close(fd);
 	return 1;
 }
+#endif
 
 int
 mtd_fixtrx(const char *mtd, size_t offset)