lib/vsprintf: Deduplicate pointer_string()

lib/vsprintf: Deduplicate pointer_string()

There is an exact code at the end of ptr_to_id().
Replace it by calling pointer_string() directly.

This is followup to the commit ad67b74d2469 ("printk: hash addresses
printed with %p").

Cc: Tobin C. Harding <me@tobin.cc>
Link: http://lkml.kernel.org/r/20180216210711.79901-6-andriy.shevchenko@linux.intel.com
To: "Tobin C . Harding" <me@tobin.cc>
To: linux@rasmusvillemoes.dk
To: Joe Perches <joe@perches.com>
To: linux-kernel@vger.kernel.org
To: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>