rtos: use struct member names instead of comments

rtos: use struct member names instead of comments

This is more readable, and as a bonus the compiler will help out if the
definition of the struct changes.

Change-Id: Ibf660134d9900173f6592407d5cc2203654a4a1b
Signed-off-by: Tim Newsome <tim@sifive.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/6659
Tested-by: jenkins
Reviewed-by: Tarek BOCHKATI <tarek.bouchkati@gmail.com>
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>