staging: comedi: comedi_buf: comedi_buf_memcpy_from() remove 'offset' param

This parameter is always passed as '0'. Remove the unnecessary parameter.

This allows removing the unnecessary check of the read_ptr overflow.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>