Dell platform with ALC298.
system enter to runtime suspend. Headphone had noise.
Let Headset Mic not shutup will solve this issue.

[ Fixed minor coding style issues by tiwai ]
Signed-off-by: Kailang Yang <kailang@realtek.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>