kbuild: remove meaningless parameter to $(call if_changed_rule,dtc)

This is a remnant of commit 78046fab ("kbuild: determine the output
format of DTC by the target suffix").

The parameter "yaml" is meaningless because cmd_dtc no loner takes $(2).
Reported-by: Rob Herring <robh@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

scripts/Makefile.lib

@@ -352,7 +352,7 @@ define rule_dtc
 endef
 
 $(obj)/%.dt.yaml: $(src)/%.dts $(DTC) $(DT_TMP_SCHEMA) FORCE
-	$(call if_changed_rule,dtc,yaml)
+	$(call if_changed_rule,dtc)
 
 dtc-tmp = $(subst $(comma),_,$(dot-target).dts.tmp)