ar71xx: more consistent image file names for TP-Link TL-WR940N (#1071)

The TL-WR940N doesn't have detachable antennas. Make v1-v3 match v4.

targets/ar71xx-tiny

@@ -51,13 +51,13 @@ device tp-link-tl-wr941n-nd-v2 tl-wr941nd-v2
 device tp-link-tl-wr941n-nd-v3 tl-wr941nd-v3
 
 device tp-link-tl-wr941n-nd-v4 tl-wr941nd-v4
-alias tp-link-tl-wr940n-nd-v1
+alias tp-link-tl-wr940n-v1
 
 device tp-link-tl-wr941n-nd-v5 tl-wr941nd-v5
-alias tp-link-tl-wr940n-nd-v2
+alias tp-link-tl-wr940n-v2
 
 device tp-link-tl-wr941n-nd-v6 tl-wr941nd-v6
-alias tp-link-tl-wr940n-nd-v3
+alias tp-link-tl-wr940n-v3
 
 device tp-link-tl-wr940n-v4 tl-wr940n-v4
 factory -squashfs-factory${GLUON_REGION:+-${GLUON_REGION}} .bin