Input: pxrc - do not store unneeded data in driver structure

There is no need to store data buffer size, pointer to the buffer, or endpoint
address in pxrc structure, as they are either only needed during setup, or are
available from elsewhere.

Reviewed-by: Marcus Folkesson <marcus.folkesson@gmail.com>
Tested-by: Marcus Folkesson <marcus.folkesson@gmail.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>