rpmsg: char: Fix rpmsg_eptdev structure documentation

rpmsg: char: Fix rpmsg_eptdev structure documentation

Add missing @ tags for some rpmsg_eptdev structure parameters.

This fixes warning messages on build:
drivers/rpmsg/rpmsg_char.c:75: warning: Function parameter or struct member 'remote_flow_restricted' not described in 'rpmsg_eptdev'
drivers/rpmsg/rpmsg_char.c:75: warning: Function parameter or struct member 'remote_flow_updated' not described in 'rpmsg_eptdev'

Fixes: 5550201c0fe2 ("rpmsg: char: Add RPMSG GET/SET FLOWCONTROL IOCTL support")
Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@foss.st.com>
Link: https://lore.kernel.org/r/20240517165654.427746-1-arnaud.pouliquen@foss.st.com
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>