vsprintf: fix data type of variable in string_nocheck()

This patch fixes data type of precision with int.
The precision is declared as signed int in struct printf_spec.

Link: http://lkml.kernel.org/r/040301d51f60$b4959100$1dc0b300$@samsung.com
To: <andriy.shevchenko@linux.intel.com>
To: <geert+renesas@glider.be>
To: <rostedt@goodmis.org>
To: <me@tobin.cc>
Signed-off-by: Youngmin Nam <youngmin.nam@samsung.com>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>