py-smbus/Module.mk: Install with PREFIX defined

If we are building to a defined destdir py-smbus is going to ignore this
and try install to the actual root. This breaks packaging setups as the
install section would fail.

Signed-off-by: Morten Linderud <morten@linderud.pw>
Signed-off-by: Jean Delvare <jdelvare@suse.de>

py-smbus/Module.mk

@@ -22,7 +22,7 @@ clean-python:
 	rm -rf py-smbus/build
 
 install-python:
-	$(DISTUTILS) install
+	$(DISTUTILS) install --prefix="$(PREFIX)"
 
 all: all-python