[ALSA] ASoC - mixer name changes for older OSS app support

This patch suggested by Richard Purdie changes the names of some WM8731
and WM8750 mixers so that they will be recognised by some older OSS
mixer apps.
Changes:-
 o WM8731 Playback changed to Master Playback
 o WM8750 Out1 changed to Headphone
 o WM8750 Out2 changed to Speaker

Signed-off-by: Liam Girdwood <lg@opensource.wolfsonmicro.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>