srcu: Fix the comparision in srcu_invl_snp_seq()

A grace-period sequence number contains two fields: counter and
state.  SRCU_SNP_INIT_SEQ provides a guaranteed invalid value for
grace-period sequence numbers in newly allocated srcu_node structures'
->srcu_have_cbs[] and ->srcu_gp_seq_needed_exp fields.  The point of the
comparison in srcu_invl_snp_seq() is not to detect invalid grace-period
sequence numbers in general, but rather to detect a newly allocated
srcu_node structure whose ->srcu_have_cbs[] and ->srcu_gp_seq_needed_exp
fields need to be brought into line with the srcu_struct structure's
->srcu_gp_seq field.

This commit therefore causes srcu_invl_snp_seq() to compare both fields
of the specified grace-period sequence number.

Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: <rcu@vger.kernel.org>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>