usb: gadget: fsl_qe_udc: fix IS_ERR_VALUE usage

IS_ERR_VALUE macro should be used only with unsigned long type.
Otherwise it can work incorrectly.

The patch follows conclusion from discussion on LKML [1][2].

[1]: http://permalink.gmane.org/gmane.linux.kernel/2120927
[2]: http://permalink.gmane.org/gmane.linux.kernel/2150581



Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>