usb: dwc3: imx: avoid calling imx suspend/resume callbacks twice

If a runtime suspend is executed followed by a system suspend, the driver
may invoke dwc3_imx_suspend() twice, which causes enable_irq() to be
called twice as well. This leads to an unbalanced IRQ state and may
trigger warnings or malfunction. Prevent this by checking the pm_suspended
flag before running the imx suspend/resume path.

Fixes: 76fc9452a6bf ("usb: dwc3: introduce flatten model driver of i.MX Soc")
Signed-off-by: Xu Yang <xu.yang_2@nxp.com>
Acked-by: Thinh Nguyen <Thinh.Nguyen@synopsys.com>
Link: https://patch.msgid.link/20260317030546.1665206-1-xu.yang_2@nxp.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>