usb: chipidea: host: Improve port index sanitizing

Coverity from Synopsys complains "Illegal address computation (OVERRUN)"
on status_reg.

After below code executed,

port_index = wIndex & 0xff;
port_index -= (port_index > 0);

the static analysis tool see the value of port_index is now between 0 and
254 (inclusive).

However, ehci_def.h define port_status as below:

#define HCS_N_PORTS_MAX 15
u32 port_status[HCS_N_PORTS_MAX];

So the tool think illegal array pointer may be obtained.

status_reg = &ehci->regs->port_status[port_index];

This will follow "846cbf98cbef USB: EHCI: Improve port index sanitizing" to
improve port index sanitizing.

Signed-off-by: Xu Yang <[e-mail]>
Acked-by: Peter Chen <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/chipidea/host.c

···
 	struct device *dev = hcd->self.controller;
 	struct ci_hdrc *ci = dev_get_drvdata(dev);
 
-	port_index = wIndex & 0xff;
-	port_index -= (port_index > 0);
+	/*
+	 * Avoid out-of-bounds values while calculating the port index
+	 * from wIndex. The compiler doesn't like pointers to invalid
+	 * addresses, even if they are never used.
+	 */
+	port_index = (wIndex - 1) & 0xff;
+	if (port_index >= HCS_N_PORTS_MAX)
+		port_index = 0;
 	status_reg = &ehci->regs->port_status[port_index];
 
 	spin_lock_irqsave(&ehci->lock, flags);