platform/mellanox: mlxbf-pmc: Fix potential buffer overflows

Replace sprintf with sysfs_emit where possible.
Size check in mlxbf_pmc_event_list_show should account for "\0".

Fixes: 1a218d31

 ("platform/mellanox: mlxbf-pmc: Add Mellanox BlueField PMC driver")
Signed-off-by: Shravan Kumar Ramani <shravankr@nvidia.com>
Reviewed-by: Vadim Pasternak <vadimp@nvidia.com>
Reviewed-by: David Thompson <davthompson@nvidia.com>
Link: https://lore.kernel.org/r/bef39ef32319a31b32f999065911f61b0d3b17c3.1693917738.git.shravankr@nvidia.com


Signed-off-by: Hans de Goede <hdegoede@redhat.com>