sxmo_audioout: use existing env vars for audio devices

If the env variables in this script are set, use those values. Else it
defaults to using the values set before this patch.

Signed-off-by: Anjandev Momi <anjan@momi.ca>

scripts/core/sxmo_audioout.sh

@@ -5,9 +5,9 @@ ARG="$1"
 # shellcheck source=scripts/core/sxmo_common.sh
 . "$(dirname "$0")/sxmo_common.sh"
 
-SPEAKER="Line Out"
+${SPEAKER:-"Line Out"}
-HEADPHONE="Headphone"
+${HEADPHONE:-"Headphone"}
-EARPIECE="Earpiece"
+${EARPIECE:-"Earpiece"}
 
 amixer set "$SPEAKER" mute
 amixer set "$HEADPHONE" mute