[SCSI] ncr53c8xx: div reaches -1

With while(--div >= 0) { ... } div reaches -1.
Signed-off-by: NRoel Kluin <roel.kluin@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NJames Bottomley <James.Bottomley@HansenPartnership.com>

drivers/scsi/ncr53c8xx.c

@@ -5444,7 +5444,7 @@ static void ncr_getsync(struct ncb *np, u_char sfac, u_char *fakp, u_char *scntl
 	**	input speed faster than the period.
 	*/
 	kpc = per * clk;
-	while (--div >= 0)
+	while (--div > 0)
 		if (kpc >= (div_10M[div] << 2)) break;
 
 	/*