ARM: OMAP2+: wakeupgen: Add comment for unhandled FROZEN transitions

FROZEN hotplug notifiers are not handled and do not have to be. Insert
a comment to remember that the lack of the FROZEN transitions is no
accident.

Cc: Tony Lindgren <tony@atomide.com>
Cc: Santosh Shilimkar <ssantosh@kernel.org>
Cc: linux-omap@vger.kernel.org
Signed-off-by: Anna-Maria Gleixner <anna-maria@linutronix.de>
Acked-by: Santosh Shilimkar <ssantosh@kernel.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>