usb: dwc3: gadget: fix IRQ storm on invalid event buffer count

In the Linux kernel, the following vulnerability has been resolved:

usb: dwc3: gadget: fix IRQ storm on invalid event buffer count

When dwc3_check_event_buf() reads a GEVNTCOUNT value exceeding the
event buffer length, commit 63ccd26cd1f6 ("usb: dwc3: gadget: check
that event count does not exceed event buffer length") returns IRQ_NONE
without writing back GEVNTCOUNT. Since the DWC3 interrupt is
level-triggered, the uncleared IRQ source keeps the line asserted,
causing a tight IRQ storm that accumulates 99,900 unhandled interrupts
and triggers spurious.c:184 BUG -> kernel panic.

The resulting call stack:
__report_bad_irq+0xac/0xc8
note_interrupt+0x340/0x468
handle_irq_event+0xac/0xc0
handle_fasteoi_irq+0x120/0x228
gic_handle_irq+0x68/0x108
...
kernel BUG at kernel/irq/spurious.c:184

To reproduce, write a bogus value exceeding the event buffer length
directly to the GEVNTCOUNT register:

devmem <DWC3_BASE + 0xc40c> 4 0x1004

Write the bogus count back to GEVNTCOUNT to clear the IRQ source,
consistent with the stale event clearing pattern in
dwc3_event_buffers_setup(), and schedule error recovery to
reinitialize the controller.