tty: hvc_iucv: fix off-by-one in number of supported devices

[ Upstream commit f2a880e ]

MAX_HVC_IUCV_LINES == HVC_ALLOC_TTY_ADAPTERS == 8.
This is the number of entries in:
  static struct hvc_iucv_private *hvc_iucv_table[MAX_HVC_IUCV_LINES];

Sometimes hvc_iucv_table[] is limited by:
(a)	if (num > hvc_iucv_devices) // for error detection
or
(b)	for (i = 0; i < hvc_iucv_devices; i++) // in 2 places
(so these 2 don't agree; second one appears to be correct to me.)

hvc_iucv_devices can be 0..8. This is a counter.
(c)	if (hvc_iucv_devices > MAX_HVC_IUCV_LINES)

If hvc_iucv_devices == 8, (a) allows the code to access hvc_iucv_table[8].
Oops.

Fixes: 44a01d5 ("[S390] s390/hvc_console: z/VM IUCV hypervisor console support")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://patch.msgid.link/20260130072939.1535869-1-rdunlap@infradead.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: rddunlap

drivers/tty/hvc/hvc_iucv.c

@@ -131,7 +131,7 @@ static struct iucv_handler hvc_iucv_handler = {
  */
 static struct hvc_iucv_private *hvc_iucv_get_private(uint32_t num)
 {
-	if (num > hvc_iucv_devices)
+	if (num >= hvc_iucv_devices)
 		return NULL;
 	return hvc_iucv_table[num];
 }