hw/sd/omap_mmc: Remove unused coverswitch qemu_irq

hw/sd/omap_mmc: Remove unused coverswitch qemu_irq

The coverswitch qemu_irq is never connected to anything, and the only thing
we do with it is set it in omap_mmc_reset(). Remove it.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20250128104519.3981448-8-peter.maydell@linaro.org>
[PMD: Remove unused 'coverswitch' field]
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>