The microphone mute led on the Latitude E5550 can't work. We need to
apply DELL_WMI_MIC_MUTE_LED quirk to this machine.

The machine uses alc293 codec and already applied the quirk
ALC293_FIXUP_DELL1_MIC_NO_PRESENCE through pin_fixup_tbl[].

Here we just let DELL_WMI_MIC_MUTE_LED be chained to
ALC269_FIXUP_HEADSET_MODE, then the machine will have these
quirks ALC293_FIXUP_DELL1_MIC_NO_PRESENCE-->
ALC269_FIXUP_HEADSET_MODE-->ALC255_FIXUP_DELL_WMI_MIC_MUTE_LED.

BugLink: https://bugs.launchpad.net/bugs/1381856Reported-and-tested-by: NPo-Hsu Lin <po-hsu.lin@canonical.com>
Signed-off-by: NHui Wang <hui.wang@canonical.com>
Signed-off-by: NTakashi Iwai <tiwai@suse.de>