cmd/internal/obj: convert unicode C to ASCII C

Hex before: d0 a1
Hex after: 43

Not sure where that came from.

Change-Id: I189e7e21f8faf480ba72846b956a149976f720f8
Reviewed-on: https://go-review.googlesource.com/109777Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/internal/obj/x86/asm6.go

@@ -3785,7 +3785,7 @@ func (ab *AsmBuf) doasm(ctxt *obj.Link, cursym *obj.LSym, p *obj.Prog) {
 		ab.Put1(byte(pre))
 	}
 
-	// Сhecks to warn about instruction/arguments combinations that
+	// Checks to warn about instruction/arguments combinations that
 	// will unconditionally trigger illegal instruction trap (#UD).
 	switch p.As {
 	case AVGATHERDPD,