bfin: Fix typo in arch_cpu_idle()

Introduced by commit 25d67f86 ("bfin: Use generic idle loop").

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Cc: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Cc: Magnus Damm <magnus.damm@gmail.com>
Cc: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>