i40e: fix unconditional execution of cpu_to_le16()

The commit 3092e5e4cc79 ("i40e: add little endian conversion for
checksum") fixed the checksum bug on big-endian architecture.

But we should not execute cpu_to_le16() unconditionally. Thus, put
cpu_to_le16() under certain condition.

Cc: Jesse Brandeburg <jesse.brandeburg@intel.com>
Cc: Paul M Stillwell Jr <paul.m.stillwell.jr@intel.com>
Signed-off-by: Jean Sacren <sakiwit@gmail.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/i40e/i40e_nvm.c

@@ -569,10 +569,11 @@ i40e_status i40e_update_nvm_checksum(struct i40e_hw *hw)
 	__le16 le_sum;
 
 	ret_code = i40e_calc_nvm_checksum(hw, &checksum);
-	le_sum = cpu_to_le16(checksum);
-	if (!ret_code)
+	if (!ret_code) {
+		le_sum = cpu_to_le16(checksum);
 		ret_code = i40e_write_nvm_aq(hw, 0x00, I40E_SR_SW_CHECKSUM_WORD,
 					     1, &le_sum, true);
+	}
 
 	return ret_code;
 }