[AArch64 costs] Fixup to costing of FNMUL

gcc/

	* config/aarch64/aarch64.c (aarch64_rtx_mult_cost): Fix FNMUL case.



git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@210512 138bc75d-0d04-0410-961f-82ee72b054a4