usbtouchscreen: use endpoint address from endpoint descriptor

use the endpoint address from the endpoint descriptor instead of the hardcoding
it to 0x81. at least some ITM based screen use a different address and don't work
without this.

Signed-off-by: Daniel Ritz <daniel.ritz@gmx.ch>
Cc: Ralf Lehmann <ralf@lehmann.cc>
Cc: J.P. Delport <jpdelport@csir.co.za>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>