fm10k: use macro to avoid passing the array and size separately

Avoid potential bugs with fm10k_add_stat_strings and
fm10k_add_ethtool_stats by using a macro to calculate the ARRAY_SIZE
when passing. This helps ensure that the size is always correct.

Note that it assumes we only pass static const fm10k_stat arrays, and
that evaluation of the argument won't have side effects.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Krishneil Singh <krishneil.k.singh@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>