genirq: Bump the size of the local variable for sprintf()

GCC is not happy about a sprintf() call on a buffer that might be too small
for the given formatting string.

kernel/irq/debugfs.c:233:26: warning: 'sprintf' may write a terminating nul past the end of the destination [-Wformat-overflow=]

Fix this by bumping the size of the local variable for sprintf().

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20250515085516.2913290-1-andriy.shevchenko@linux.intel.com
Closes: https://lore.kernel.org/oe-kbuild-all/202505151057.xbyXAbEn-lkp@intel.com/