wifi: ath5k: Use platform_get_irq() to get the interrupt

As of commit a1a2b712 ("of/platform: Drop static setup of IRQ
resource from DT core"), we need to use platform_get_irq() instead of
platform_get_resource() to get our IRQs because
platform_get_resource() simply won't get them anymore.

This was already fixed in several other Atheros WiFi drivers,
apparently in response to Zeal Robot reports. An example of another
fix is commit 9503a1fc ("ath9k: Use platform_get_irq() to get the
interrupt"). ath5k seems to have been missed in this effort, though.

Fixes: a1a2b712

 ("of/platform: Drop static setup of IRQ resource from DT core")
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20230201084131.v2.2.Ic4f8542b0588d7eb4bc6e322d4af3d2064e84ff0@changeid