cmd/vet: fix line number in asm errors
cmd/vet: fix line number in asm errors

Before:
: asm_amd64.s:16: [amd64] invalid offset new+16(FP); expected new+8(FP)
: asm_amd64.s:26: [amd64] invalid offset new+16(FP); expected new+8(FP)

After:
asm_amd64.s:16: [amd64] invalid offset new+16(FP); expected new+8(FP)
asm_amd64.s:26: [amd64] invalid offset new+16(FP); expected new+8(FP)

LGTM=r
R=r
CC=golang-codereviews
https://codereview.appspot.com/91510043

webfd/go-zh.tools,bryanxu/go-zh.tools,d0f/go-zh.tools,d0f/go-zh.tools,bryanxu/go-zh.tools,d0f/go-zh.tools,webfd/go-zh.tools,skyportsystems/go.tools,bryanxu/go-zh.tools,skyportsystems/go.tools,skyportsystems/go.tools,d0f/go-zh.tools,d0f/go-zh.tools,webfd/go-zh.tools,skyportsystems/go.tools,skyportsystems/go.tools,8limbs/gotools,bryanxu/go-zh.tools,8limbs/gotools,bryanxu/go-zh.tools,webfd/go-zh.tools,8limbs/gotools,webfd/go-zh.tools