soc: ti: k3-ringacc: Fixup documentation errors

soc: ti: k3-ringacc: Fixup documentation errors

Fixup couple of misses in documentation. This squashes the following
warnings:
drivers/soc/ti/k3-ringacc.c:135: warning: Function parameter or member 'tdown_complete' not described in 'k3_ring_state'
drivers/soc/ti/k3-ringacc.c:238: warning: expecting prototype for struct k3_ringacc. Prototype was for struct k3_ringacc_soc_data instead

While at this, replace "w/a" to indicate workaround to help clarify.

Cc: Peter Ujfalusi <peter.ujfalusi@gmail.com>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://lore.kernel.org/r/20230621023442.275128-1-nm@ti.com
Signed-off-by: Nishanth Menon <nm@ti.com>