ice: re-order ice_mbx_reset_snapshot function

A future change is going to refactor the VF mailbox overflow detection
logic, including modifying ice_mbx_reset_snapshot and its callers. To make
this change easier to review, first move the ice_mbx_reset_snapshot
function higher in the ice_vf_mbx.c file.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Michal Swiatkowski <michal.swiatkowski@linux.intel.com>
Tested-by: Marek Szlosek <marek.szlosek@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>