Put the sed flag in the right place.

Index: lib/libbamf-private/Makefile.in
--- lib/libbamf-private/Makefile.in.orig
+++ lib/libbamf-private/Makefile.in
@@ -736,7 +736,7 @@ bamf-gdbus-generated.c: org.ayatana.bamf.xml
 	--interface-prefix org.ayatana.bamf \
 	$<; \
 	# Adding '_' prefix to generated private functions \
-	$(SED) "s/bamf_dbus/_bamf_dbus/g" -i \
+	$(SED) -i "s/bamf_dbus/_bamf_dbus/g" \
 	$@ $(shell basename $@ .c).h
 
 .NOTPARALLEL:
@@ -748,7 +748,7 @@ bamf-gdbus-view-generated.c: org.ayatana.bamf.view.xml
 	--interface-prefix org.ayatana.bamf \
 	$<; \
 	# Adding '_' prefix to generated private functions \
-	$(SED) "s/bamf_dbus_item/_bamf_dbus_item/g" -i \
+	$(SED) -i "s/bamf_dbus_item/_bamf_dbus_item/g" \
 	$@ $(shell basename $@ .c).h
 
 # Tell versions [3.59,3.63) of GNU make to not export all variables.