[input] Modernize codebase by replacing NULL with nullptr

Fixes -Wzero-as-null-pointer-constant warning.

Test: m
Bug: 68236239
Change-Id: I8882234efd2a0b3ef27472d3f5d4e9c69c6e7b37
diff --git a/libs/input/KeyLayoutMap.cpp b/libs/input/KeyLayoutMap.cpp
index 2b2f13e..c440078 100644
--- a/libs/input/KeyLayoutMap.cpp
+++ b/libs/input/KeyLayoutMap.cpp
@@ -117,7 +117,7 @@
             return &mKeysByScanCode.valueAt(index);
         }
     }
-    return NULL;
+    return nullptr;
 }
 
 status_t KeyLayoutMap::findScanCodesForKey(int32_t keyCode, Vector<int32_t>* outScanCodes) const {