xhci: fixup incorrect memset size parameter when clearing up DbC on exit.

Incorrect size was given to memset when zeroing the DbC endpoint
structures on exit. Use element size * ARRAY_SIZE to fix it

Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Fixes: dfba2174 ("usb: xhci: Add DbC support in xHCI driver")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>