usb: gadget: tegra-xudc: Fix error check in tegra_xudc_powerdomain_init()

dev_pm_domain_attach_by_name() may return NULL in some cases,
so IS_ERR() doesn't meet the requirements. Thus fix it.

Fixes: 49db4272 ("usb: gadget: Add UDC driver for tegra XUSB device mode controller")
Signed-off-by: Tang Bin <tangbin@cmss.chinamobile.com>
Link: https://lore.kernel.org/r/20220525135332.23144-1-tangbin@cmss.chinamobile.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>