at91bootstrap: no board name check when 'make source' is used

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

boot/at91bootstrap/at91bootstrap.mk

@@ -56,8 +56,11 @@ at91bootstrap-dirclean:
 ifeq ($(BR2_TARGET_AT91BOOTSTRAP),y)
 TARGETS+=at91bootstrap
 
-# we NEED a board name
+# we NEED a board name unless we're at make source
+ifeq ($(filter source,$(MAKECMDGOALS)),)
 ifeq ($(AT91BOOTSTRAP_BOARD),)
 $(error No AT91Bootstrap board name set. Check your BR2_TARGET_AT91BOOTSTRAP_BOARD setting)
 endif
 endif
+
+endif