doc: rcu: update printed dynticks counter bits

The stall warning prints 16 bits since commit 1714767
("context_tracking: Convert state to atomic_t").

Fixes: 1714767 ("context_tracking: Convert state to atomic_t")
Signed-off-by: Baruch Siach <[email protected]>
Reviewed-by: "Paul E. McKenney" <[email protected]>
Signed-off-by: Neeraj Upadhyay <[email protected]>
Signed-off-by: Frederic Weisbecker <[email protected]>

Author: baruchsiach

Documentation/RCU/stallwarn.rst

@@ -249,7 +249,7 @@ ticks this GP)" indicates that this CPU has not taken any scheduling-clock
 interrupts during the current stalled grace period.
 
 The "idle=" portion of the message prints the dyntick-idle state.
-The hex number before the first "/" is the low-order 12 bits of the
+The hex number before the first "/" is the low-order 16 bits of the
 dynticks counter, which will have an even-numbered value if the CPU
 is in dyntick-idle mode and an odd-numbered value otherwise.  The hex
 number between the two "/"s is the value of the nesting, which will be