runtime: update comment that was missed in CL 6584

Change-Id: Ie5f70af7e673bb2c691a45c28db2c017e6cddd4f
Reviewed-on: https://go-review.googlesource.com/16833Reviewed-by: Minux Ma <minux@golang.org>

src/runtime/sys_openbsd_amd64.s

@@ -306,7 +306,7 @@ TEXT runtime·sigaltstack(SB),NOSPLIT,$-8
 
 // set tls base to DI
 TEXT runtime·settls(SB),NOSPLIT,$0
-	// adjust for ELF: wants to use -16(FS) and -8(FS) for g and m
+	// adjust for ELF: wants to use -8(FS) for g
 	ADDQ	$8, DI
 	MOVQ	$329, AX		// sys___settcb
 	SYSCALL