wpa-supplicant: Match package override to PACKAGES for pkg_postinst

In PACKAGES, ${PN} is used so it makes sense for the pkg_postinst variable
override to match that else it causes user confusion.

[YOCTO #14616]

(From OE-Core rev: ae9094d45bbfff377bd542939e12a8451a4959b6)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-connectivity/wpa-supplicant/wpa-supplicant_2.9.bb

@@ -108,7 +108,7 @@ do_install () {
 	install -m 0644 ${WORKDIR}/99_wpa_supplicant ${D}/etc/default/volatiles
 }
 
-pkg_postinst:wpa-supplicant () {
+pkg_postinst:${PN} () {
 	# If we're offline, we don't need to do this.
 	if [ "x$D" = "x" ]; then
 		killall -q -HUP dbus-daemon || true