Fix use of wrong variable in pg_receivewal's get_destination_dir().

The global variable wrongly used is always the one passed to
get_destination_dir(), so there currently are no negative consequences.

Author: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Discussion: https://postgr.es/m/CALj2ACUT0C2LQwhyLXTQdj8T9SxZa5j7cmu-UOz0cZ8_D5edjg@mail.gmail.com

src/bin/pg_basebackup/pg_receivewal.c

@@ -240,7 +240,7 @@ get_destination_dir(char *dest_folder)
 	dir = opendir(dest_folder);
 	if (dir == NULL)
 	{
-		pg_log_error("could not open directory \"%s\": %m", basedir);
+		pg_log_error("could not open directory \"%s\": %m", dest_folder);
 		exit(1);
 	}