cmd/compile/internal/gc: remove oconv(op, 0) calls

Updates #15462

Automatic refactor with sed -e.

Replace all oconv(op, 0) to string conversion with the raw op value
which fmt's %v verb can print directly.

The remaining oconv(op, FmtSharp) will be replaced with op.GoString and
%#v in the next CL.

Change-Id: I5e2f7ee0bd35caa65c6dd6cb1a866b5e4519e641
Reviewed-on: https://go-review.googlesource.com/22499
Run-TryBot: Dave Cheney <dave@cheney.net>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
diff --git a/src/cmd/compile/internal/gc/gen.go b/src/cmd/compile/internal/gc/gen.go
index 6fb27cf..275e6a7 100644
--- a/src/cmd/compile/internal/gc/gen.go
+++ b/src/cmd/compile/internal/gc/gen.go
@@ -218,7 +218,7 @@
 func cgen_proc(n *Node, proc int) {
 	switch n.Left.Op {
 	default:
-		Fatalf("cgen_proc: unknown call %v", oconv(n.Left.Op, 0))
+		Fatalf("cgen_proc: unknown call %v", n.Left.Op)
 
 	case OCALLMETH:
 		cgen_callmeth(n.Left, proc)