wifi: wilc1000: convert list management to RCU

wilc1000 driver currently uses SRCU API to manage vif list. There is no
real reason to use SRCU API here, and it makes things slightly more
complicated (we need to handle a SRCU index as well as a srcu_struct) than
classical RCU.

Switch SRCU APIs to RCU APIs.

Signed-off-by: Alexis Lothoré <alexis.lothore@bootlin.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://msgid.link/20240410-wilc_srcu_to_rcu-v1-2-a9ff5b10feaa@bootlin.com