greybus: audio: topology: Use csize while computing next_ptr in parser

Size of control elements vary in case of enumerated controls. As a
preparation to enable enumerated control in topology parser, this patch
uses csize while parsing controls & wsize while parsing widgets & its
control to update next pointer.

Signed-off-by: Vaibhav Agarwal <vaibhav.agarwal@linaro.org>
Reviewed-by: Mark Greer <mark.greer@animalcreek.com>
Signed-off-by: Alex Elder <elder@linaro.org>