sdhci: Fix misuse of qemu_free_irqs()

It does a g_free() on the pointer, so don't pass a local &foo reference.

Reviewed-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Andreas Färber <afaerber@suse.de>