ifcvt: cleanup if_info->cond usage in noce_try_cond_zero_arith

ifcvt: cleanup if_info->cond usage in noce_try_cond_zero_arith

Since r16-6332-g2a84a753afcf37, if_info->cond is not used indirectly any more
for creating the conditional. So this patch stops doing the swap and fixes up
so the case where if_info->rev_cond might be null.

gcc/ChangeLog:

	* ifcvt.cc (noce_try_cond_zero_arith): Don't swap if_info->cond
	but use it directly with if_info->rev_cond.

Signed-off-by: Andrew Pinski <andrew.pinski@oss.qualcomm.com>