scsi: sym53c8xx_2: iterator underflow in sym_getsync()

BugLink: https://bugs.launchpad.net/bugs/1775771

[ Upstream commit e6f791d9 ]

We wanted to exit the loop with "div" set to zero, but instead, if we
don't hit the break then "div" is -1 when we finish the loop.  It leads
to an array underflow a few lines later.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Acked-by: Matthew Wilcox <mawilcox@microsoft.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

drivers/scsi/sym53c8xx_2/sym_hipd.c

@@ -536,7 +536,7 @@ sym_getsync(struct sym_hcb *np, u_char dt, u_char sfac, u_char *divp, u_char *fa
 	 *  Look for the greatest clock divisor that allows an 
 	 *  input speed faster than the period.
 	 */
-	while (div-- > 0)
+	while (--div > 0)
 		if (kpc >= (div_10M[div] << 2)) break;
 
 	/*