x86/events/amd/iommu: Increase IOMMU_NAME_SIZE

The init_one_iommu() takes an unsigned int argument that can't be checked for
the boundaries at compile time and GCC complains about that when build with
`make W=1`:

arch/x86/events/amd/iommu.c:441:53: note: directive argument in the range [0, 4294967294]
arch/x86/events/amd/iommu.c:441:9: note: ‘snprintf’ output between 12 and 21 bytes into a destination of size 16

Increase the size to cover all possible cases.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20250210193412.483233-1-andriy.shevchenko@linux.intel.com