cmd/internal/obj/x86: modify the threshold of assert loop for span6

Fixes: #49716

Change-Id: I7ed73f874c2ee1ee3f31c9c4428ed484167ca803
Reviewed-on: https://go-review.googlesource.com/c/go/+/366094
Reviewed-by: Cherry Mui <cherryyz@google.com>
Trust: Heschi Kreinick <heschi@google.com>

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

@@ -2174,7 +2174,7 @@ func span6(ctxt *obj.Link, s *obj.LSym, newprog obj.ProgAlloc) {
 		}
 
 		n++
-		if n > 20 {
+		if n > 1000 {
 			ctxt.Diag("span must be looping")
 			log.Fatalf("loop")
 		}