e1000e: cleanup - check return values consistently

The majority of the e1000e code checks most function return values using a
test like 'if (ret_val)' or 'if (!ret_val)' but there are a few instances
of 'if (ret_val == 0)'.  This patch converts the latter to the former for
consistency.

Signed-off-by: Bruce Allan <bruce.w.allan@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
diff --git a/drivers/net/ethernet/intel/e1000e/ethtool.c b/drivers/net/ethernet/intel/e1000e/ethtool.c
index 92d5b62..f43af46 100644
--- a/drivers/net/ethernet/intel/e1000e/ethtool.c
+++ b/drivers/net/ethernet/intel/e1000e/ethtool.c
@@ -537,7 +537,7 @@
 		ret_val = e1000_read_nvm(hw, first_word, 1, &eeprom_buff[0]);
 		ptr++;
 	}
-	if (((eeprom->offset + eeprom->len) & 1) && (ret_val == 0))
+	if (((eeprom->offset + eeprom->len) & 1) && (!ret_val))
 		/* need read/modify/write of last changed EEPROM word */
 		/* only the first byte of the word is being modified */
 		ret_val = e1000_read_nvm(hw, last_word, 1,