MAINTAINERS: Add VSPRINTF

MAINTAINERS: Add VSPRINTF

printk maintainers have been reviewing patches against vsprintf code last
few years. Most changes have been committed via printk.git last two years.

New group is used because printk() is not the only vsprintf() user.
Also the group of interested people is not the same.

Link: http://lkml.kernel.org/r/20191031133337.9306-1-pmladek@suse.com
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: linux-kernel@vger.kernel.org
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Uwe Kleine-König <uwe@kleine-koenig.org>
Cc: Joe Perches <joe@perches.com>
Cc: Sakari Ailus <sakari.ailus@linux.intel.com>
Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Acked-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>