Documentation: Fix RCU typos

Fix typos.

Signed-off-by: Bjorn Helgaas <[e-mail]>
Reviewed-by: Randy Dunlap <[e-mail]>
Signed-off-by: Jonathan Corbet <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

Documentation/RCU/lockdep.rst

···
 Like rcu_dereference(), when lockdep is enabled, RCU list and hlist
 traversal primitives check for being called from within an RCU read-side
 critical section.  However, a lockdep expression can be passed to them
-as a additional optional argument.  With this lockdep expression, these
+as an additional optional argument.  With this lockdep expression, these
 traversal primitives will complain only if the lockdep expression is
 false and they are called from outside any RCU read-side critical section.
 

Documentation/RCU/stallwarn.rst

···
 	uncommon in large datacenter.  In one memorable case some decades
 	back, a CPU failed in a running system, becoming unresponsive,
 	but not causing an immediate crash.  This resulted in a series
-	of RCU CPU stall warnings, eventually leading the realization
+	of RCU CPU stall warnings, eventually leading to the realization
 	that the CPU had failed.
 
 The RCU, RCU-sched, RCU-tasks, and RCU-tasks-trace implementations have