doc: fix quiescent state description in RCU guide
doc: fix quiescent state description in RCU guide

The quiescent state description refers to an incorrect
thread.

Fixes: 64994b56cfd7 ("rcu: add RCU library supporting QSBR mechanism")
Cc: stable@dpdk.org

Signed-off-by: Prateek Agarwal <384916bbb858c6f2eeddd2f08a45cf5990110772@cse.iitb.ac.in>
Signed-off-by: Honnappa Nagarahalli <01ccf438b971cc1d8919c8a7f18443cae9429d8b@arm.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk