syscall: fix typo in RawSyscall6 comment

Change-Id: I589a60459a3b0811da77d46428eca57c741b1184
GitHub-Last-Rev: f9ab775b9d7f869916af6de9abb7c1d5f0005f1b
GitHub-Pull-Request: golang/go#26063
Reviewed-on: https://go-review.googlesource.com/120917Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/syscall/asm_darwin_amd64.s

@@ -117,7 +117,7 @@ ok1:
 	MOVQ	$0, err+48(FP)
 	RET
 
-// func RawSyscall(trap, a1, a2, a3 uintptr) (r1, r2 uintptr, err Errno)
+// func RawSyscall6(trap, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2 uintptr, err Errno)
 TEXT	·RawSyscall6(SB),NOSPLIT,$0-80
 	MOVQ	a1+8(FP), DI
 	MOVQ	a2+16(FP), SI