rpmsg: update documentation

rpmsg_create_ept() takes struct rpmsg_channel_info chinfo as its last
argument, not a u32 value. The first two arguments are also updated.

Signed-off-by: Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>
Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Link: https://lore.kernel.org/r/20200722150927.15587-4-guennadi.liakhovetski@linux.intel.com


Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>