kb_elmo/elmopad: fix macro reference in info.json (qmk#15142)

Author: noroadsleft

keyboards/kb_elmo/elmopad/info.json

@@ -3,7 +3,7 @@
     "url": "https://github.com/kb-elmo/numpad",
     "maintainer": "kb-elmo",
     "layouts": {
-        "LAYOUT": {
+        "LAYOUT_numpad_6x4": {
             "layout": [
                 {"x":0, "y":0}, 
                 {"x":1, "y":0},