util: fix compile warnings

util: fix compile warnings

This patch fixes two compile warnings introduced by commit
64b73291 ("util: create a copy of program_name"):
1. ../lib/util.c:457:5: error: passing argument 1 of 'free'
   discards 'const' qualifier from pointer target type; And
2. ../lib/util.c:463:5: error: ISO C90 forbids mixed declarations
   and code [-Werror=declaration-after-statement] (affected only
   branch-2.3 that is C90 compliant and not the master)

Reported-By: Joe Stringer <jstringer@nicira.com>
Reported-By: Lorand Jakab <lojakab@cisco.com>
Signed-Off-By: Ansis Atteka <aatteka@nicira.com>
Acked-by: Joe Stringer <joestringer@nicira.com>