runtime: remove redundant type cast

  (*T)(unsafe.Pointer(&t)) === &t
for t of type T

Change-Id: I43c1aa436747dfa0bf4cb0d615da1647633f9536
Reviewed-on: https://go-review.googlesource.com/15656Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/runtime/symtab.go

@@ -284,7 +284,7 @@ func cfuncname(f *_func) *byte {
 	if datap == nil {
 		return nil
 	}
-	return (*byte)(unsafe.Pointer(&datap.pclntable[f.nameoff]))
+	return &datap.pclntable[f.nameoff]
 }
 
 func funcname(f *_func) string {