usb: renesas_usbhs: Flush the notify_hotplug_work

usb: renesas_usbhs: Flush the notify_hotplug_work

When performing continuous unbind/bind operations on the USB drivers
available on the Renesas RZ/G2L SoC, a kernel crash with the message
"Unable to handle kernel NULL pointer dereference at virtual address"
may occur. This issue points to the usbhsc_notify_hotplug() function.

Flush the delayed work to avoid its execution when driver resources are
unavailable.

Fixes: bc57381e6347 ("usb: renesas_usbhs: use delayed_work instead of work_struct")
Cc: stable <stable@kernel.org>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Tested-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
Link: https://lore.kernel.org/r/20250225110248.870417-4-claudiu.beznea.uj@bp.renesas.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>