nss: fix postinst script for nativesdk build

It's better to refer to binaries in postinst script with
full path which also works on SDK when
/opt/nativesysroot/usr/bin is not in PATH.

Fixes install of nativesdk-nss:

Configuring nativesdk-nss.
/var/lib/opkg/info/nativesdk-nss.postinst: line 14: signlibs.sh: not found

Signed-off-by: Mikko Rapeli <mikko.rapeli@bmw.de>
Signed-off-by: Khem Raj <raj.khem@gmail.com>

meta-oe/recipes-support/nss/nss_3.54.bb

@@ -244,13 +244,13 @@ pkg_postinst_${PN} () {
             DN=`dirname $I`
             BN=`basename $I .chk`
             FN=$DN/$BN.so
-            shlibsign -i $FN
+            ${bindir}/shlibsign -i $FN
             if [ $? -ne 0 ]; then
                 exit 1
             fi
         done
     else
-        signlibs.sh
+        ${bindir}/signlibs.sh
     fi
 }