ice: Declare functions static

ice_get_pfa_module_tlv() and ice_read_sr_word() are not being called
outside of their file. Declare them as static.

Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>