usb: musb: omap2430: add missing platform_device_put() on error in omap2430_probe()

Add the missing platform_device_put() before return from
omap2430_probe() in the error handling case.

Introduced by commit ca784be3
(usb: start using the control module driver)

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: Felipe Balbi <balbi@ti.com>