polkit-group-rule: Set S to UNPACKDIR

It only install local files from SRC_URI, so nothing is ever
unpacked into ${UNPACKDIR}/${BP} and the default S never exists, making
do_unpack warn for each of them:

  WARNING: polkit-group-rule-datetime-1.0-r0 do_unpack:
  polkit-group-rule-datetime: the directory ${UNPACKDIR}/${BP} pointed
  to by the S variable doesn't exist - please set S within the recipe to
  point to where the source has been unpacked to

Point S at ${UNPACKDIR} in the shared include, which is what oe-core
does for file-only recipes such as init-ifupdown and keymaps. This
covers polkit-group-rule-{datetime,network,udisks2} in one place; the
do_install tasks already reference ${UNPACKDIR} directly, so packaging
is unchanged.

Signed-off-by: Khem Raj <khem.raj@oss.qualcomm.com>

meta-oe/recipes-extended/polkit/polkit-group-rule.inc

@@ -1,5 +1,7 @@
 HOMEPAGE = "https://www.yoctoproject.org/"
 
+S = "${UNPACKDIR}"
+
 # polkit must prepare polkitd group
 DEPENDS += "polkit"