storage: Replace magic number with define in usb_stor_euscsi_init()

usb_stor_euscsi_init() calls usb_stor_control_msg() with timeout
argument 5000. USB_CTRL_SET_TIMEOUT is defined to be 5000 in usb.h, so
would it make sense to use that instead? Patch below if it would.

Signed-off-by: Mark Knibbs <markk@clara.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>