genbuild_h: Fix numeric comparison to remove error

Change the comparison of build_timeless from -eq to =

This was generating an error if BUILD_TIMELESS wasn't set:
util/genbuild_h/genbuild_h.sh: line 27: [: : integer expression expected

This wasn't causing the script to fail, and won't even if 'set -e' is
added to the script because the error happens inside an 'if' clause,
which is specifically excluded from failue on 'set -e'.

Change-Id: I6a4e147ece23e83ee682d72db35be9e5d4088c78
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/14080
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Alexander Couzens <lynxis@fe80.eu>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

util/genbuild_h/genbuild_h.sh

@@ -24,7 +24,7 @@ export TZ=UTC
 
 top=`dirname $0`/../..
 
-if [ "${BUILD_TIMELESS}" -eq 1 ]; then
+if [ "${BUILD_TIMELESS}" = "1" ]; then
 	GITREV=Timeless
 	TIMESOURCE="fixed"
 	DATE=0