rcu: Remove spurious instrumentation_end() in rcu_nmi_enter()

In rcu_nmi_enter(), there is an erroneous instrumentation_end() in the
second branch of the "if" statement.  Oddly enough, "objtool check -f
vmlinux.o" fails to complain because it is unable to correctly cover
all cases.  Instead, objtool visits the third branch first, which marks
following trace_rcu_dyntick() as visited.  This commit therefore removes
the spurious instrumentation_end().

Fixes: 04b25a49 ("rcu: Mark rcu_nmi_enter() call to rcu_cleanup_after_idle() noinstr")
Reported-by Neeraj Upadhyay <neeraju@codeaurora.org>
Signed-off-by: Zhouyi Zhou <zhouzhouyi@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>