ucm: Handle repeat device and modifier enables/disables

ucm: Handle repeat device and modifier enables/disables

Currently, enabling a device twice can cause it to be added to
snd_use_case_mgr_t->active_devices twice, causing the list to become a
loop and subsequent uses to result in an infinite loop.

This patch makes sure we don't enable/disable a device twice, and avoid
doing the same for modifiers.

Signed-off-by: Arun Raghavan <arun.raghavan@collabora.co.uk>
Acked-by: Liam Girdwood <lrg@ti.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>