scripts: kconfig: Fix uses of edt.compat2okay in helper functions

Check if a given 'compat' is a key in edt.compat2okay before accessing
its entry in dt_compat_on_bus() and dt_nodelabel_has_compat(), as for
a non-existing key a new entry with an empty list would be created,
and dt_compat_enabled() would then incorrectly return "y" when called
for the same 'compat'.

Signed-off-by: Andrzej Głąbek <andrzej.glabek@nordicsemi.no>

scripts/kconfig/kconfigfunctions.py

@@ -390,9 +390,10 @@ def dt_compat_on_bus(kconf, _, compat, bus):
     if doc_mode or edt is None:
         return "n"
 
-    for node in edt.compat2okay[compat]:
-        if node.on_bus is not None and node.on_bus == bus:
-            return "y"
+    if compat in edt.compat2okay:
+        for node in edt.compat2okay[compat]:
+            if node.on_bus is not None and node.on_bus == bus:
+                return "y"
 
     return "n"
 
@@ -406,9 +407,10 @@ def dt_nodelabel_has_compat(kconf, _, label, compat):
     if doc_mode or edt is None:
         return "n"
 
-    for node in edt.compat2okay[compat]:
-        if label in node.labels:
-            return "y"
+    if compat in edt.compat2okay:
+        for node in edt.compat2okay[compat]:
+            if label in node.labels:
+                return "y"
 
     return "n"