ASoC: sti: use managed regmap_field allocations

In the Linux kernel, the following vulnerability has been resolved:

ASoC: sti: use managed regmap_field allocations

The regmap_field objects allocated at player init are never freed and

may leak resources if the driver is removed.

Switch to devm_regmap_field_alloc() to automatically limit the lifetime

of the allocations the lifetime of the device.