usb: musb: ux500: use devm_ functions

This patch introduces the use of managed interfaces for clk_get and
kzalloc and removes the corresponding free function calls in the probe
and remove functions.

Signed-off-by: Himangi Saraogi <himangi774@gmail.com>
Acked-by: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Felipe Balbi <balbi@ti.com>