We've got a regression report wrt the IRQ issue related with the
power-save on a Dell machine, and disabling runtime PM works around.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=53441

Cc: <stable@vger.kernel.org> [v3.7+]
Signed-off-by: Takashi Iwai <tiwai@suse.de>