usb: musb: da8xx: Use devm in probe

Simplify things a bit by using devm functions where possible.

Signed-off-by: David Lechner <david@lechnology.com>
[b-liu@ti.com: fixed merge conflict]
Signed-off-by: Bin Liu <b-liu@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>