hw/i386/Makefile.obj: use $(PYTHON) to run .py scripts consistently

$(PYTHON) is a Make variable which is set by configure.
In all other places over the tree, .py files are run from
Makefiles using this variable, except of a single leftover
in hw/i386/Makefile.obj (and a nearby place in there uses
$(PYTHON) correctly).  Fix this leftover too.
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>
Cc: Luigi Rizzo <rizzo@iet.unipi.it>
Reviewed-by: N: Stefan Weil <sw@weilnetz.de>

hw/i386/Makefile.objs

@@ -20,7 +20,7 @@ hw/i386/%.hex: $(SRC_PATH)/hw/i386/%.dsl $(SRC_PATH)/scripts/acpi_extract_prepro
 	$(call quiet-command, cpp -P $< -o $*.dsl.i.orig, "  CPP $(TARGET_DIR)$*.dsl.i.orig")
 	$(call quiet-command, $(PYTHON) $(SRC_PATH)/scripts/acpi_extract_preprocess.py $*.dsl.i.orig > $*.dsl.i, "  ACPI_PREPROCESS $(TARGET_DIR)$*.dsl.i")
 	$(call quiet-command, $(IASL) $(call iasl-option,$(IASL),-Pn,) -vs -l -tc -p $* $*.dsl.i $(if $(V), , > /dev/null) 2>&1 ,"  IASL $(TARGET_DIR)$*.dsl.i")
-	$(call quiet-command, $(SRC_PATH)/scripts/acpi_extract.py $*.lst > $*.off, "  ACPI_EXTRACT $(TARGET_DIR)$*.off")
+	$(call quiet-command, $(PYTHON) $(SRC_PATH)/scripts/acpi_extract.py $*.lst > $*.off, "  ACPI_EXTRACT $(TARGET_DIR)$*.off")
 	$(call quiet-command, cat $*.off > $@, "  CAT $(TARGET_DIR)$@")
 else
 #IASL Not present. Restore pre-generated hex files.