USB: EHCI: Improve port index sanitizing

USB: EHCI: Improve port index sanitizing

Now that Kees Cook has added a definition for HCS_N_PORTS_MAX in
commit 72dd1843232c ("USB: EHCI: Add register array bounds to HCS
ports"), the code in ehci_hub_control() which sanitizes port index
values can be improved a little.

The idea behind this change is that it prevents a possible
out-of-bounds pointer computation, which the compiler might be able to
detect since the port_status[] array now has a fixed length rather
than a variable length.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Link: https://lore.kernel.org/r/20211002190217.GA537967@rowland.harvard.edu
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>