runtime: remove +1-1 when asking PC values

Fixes #26437

Change-Id: Id47b3bcc23ea7b7b17b55dd96b5830c48fd8d53d
Reviewed-on: https://go-review.googlesource.com/124895Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/runtime/extern.go

@@ -176,7 +176,7 @@ func Caller(skip int) (pc uintptr, file string, line int, ok bool) {
 	// what it called, so that CallersFrames can see if it "called"
 	// sigpanic, and possibly a PC for skipPleaseUseCallersFrames.
 	var rpc [3]uintptr
-	if callers(1+skip-1, rpc[:]) < 2 {
+	if callers(skip, rpc[:]) < 2 {
 		return
 	}
 	var stackExpander stackExpander