cmake: modules: dts: Fix board revision 0 overlay

Fixes an issue whereby a board revision is 0 and the overlay file
exists but would not be included

Signed-off-by: Jamie McCrae <[email protected]>

Author: nordicjm

cmake/dts.cmake

@@ -53,7 +53,7 @@ list(REMOVE_DUPLICATES
 # Drop support for NOT CONFIG_HAS_DTS perhaps?
 if(EXISTS ${DTS_SOURCE})
   set(SUPPORTS_DTS 1)
-  if(BOARD_REVISION AND EXISTS ${BOARD_DIR}/${BOARD}_${BOARD_REVISION_STRING}.overlay)
+  if(DEFINED BOARD_REVISION AND EXISTS ${BOARD_DIR}/${BOARD}_${BOARD_REVISION_STRING}.overlay)
     list(APPEND DTS_SOURCE ${BOARD_DIR}/${BOARD}_${BOARD_REVISION_STRING}.overlay)
   endif()
 else()