USB: fix ep_config to return correct value

This patch fixes ep_config to return correct value. Without patch
ep_config returns submitted lenght minus 4 on succes. With this
patch applied, whole submitted lenght is returned.

ep_config parses submitted data and if buffer starts with (int) 1
it is parsed, otherwise error is reported. Problem is that ep_config
returns size of buffer minus 4 on success. I think that size of buffer
should be returned instead, because there were no problems and
all data were processed.

Signed-off-by: Milan Svoboda <msvoboda@ra.rockwell.com>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>