ice: fix incorrect size description of ice_get_nvm_version

The function comment for ice_get_nvm_version indicated that the ver_hi
and ver_lo values were 16 bits. In fact, they are only uint8_t values,
meaning that they have a maximum size of 8 bits. Fix the comment to
match the correct size.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>