Makefile: fix distclean removal of $(O)

The distclean target no longer removes the "output" directory for
in-tree builds, because $(O) is no longer just "output" in that
case. Change the test to be against "$(CURDIR)/output", to match
the O setting, and a similar test elsewhere in the same Makefile.

Signed-off-by: Danomi Manchego <danomimanchego123@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

Makefile

@@ -928,7 +928,7 @@ clean:
 		$(LEGAL_INFO_DIR) $(GRAPHS_DIR)
 
 distclean: clean
-ifeq ($(O),output)
+ifeq ($(O),$(CURDIR)/output)
 	rm -rf $(O)
 endif
 	rm -rf $(TOPDIR)/dl $(BR2_CONFIG) $(CONFIG_DIR)/.config.old $(CONFIG_DIR)/..config.tmp \