staging: usbip: bugfix for stack corruption on 64-bit architectures

Previously a 6 byte array (buf) was erroneously cast to a 8 byte long
(event_bits) on 64-bit architectures which caused a stack corruption.

Signed-off-by: Bart Westgeest <bart@elbrys.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>