usb: gadget: s3c-hsudc: Use devm_* functions

devm_* functions are used to replace kzalloc, request_mem_region, ioremap
clk_get and request_irq functions in probe call. With the usage of devm_*
functions explicit freeing and unmapping is not required.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Felipe Balbi <balbi@ti.com>