[SCSI] esp_scsi: Make cur_residue and tot_residue signed.

Many of the overflow checks test whether the value has
gone negative, and we want to retain such checks.

Reported by Julia Lawall.
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

drivers/scsi/esp_scsi.h

@@ -240,9 +240,9 @@ struct esp_cmd_priv {
 		int		num_sg;
 	} u;
 
-	unsigned int		cur_residue;
+	int			cur_residue;
 	struct scatterlist	*cur_sg;
-	unsigned int		tot_residue;
+	int			tot_residue;
 };
 #define ESP_CMD_PRIV(CMD)	((struct esp_cmd_priv *)(&(CMD)->SCp))