usb: chipidea: host: Improve port index sanitizing

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 <xu.yang_2@nxp.com>
Acked-by: Peter Chen <peter.chen@kernel.org>
Link: https://lore.kernel.org/r/20241202083453.704533-1-xu.yang_2@nxp.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>