USB: EHCI: declare hostpc register as zero-length array

The HOSTPC extension registers found in some EHCI implementations form
a variable-length array, with one element for each port.  Therefore
the hostpc field in struct ehci_regs should be declared as a
zero-length array, not a single-element array.

This fixes a problem reported by UBSAN.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Reported-by: Wilfried Klaebe <linux-kernel@lebenslange-mailadresse.de>
Tested-by: Wilfried Klaebe <linux-kernel@lebenslange-mailadresse.de>
CC: <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>