staging: r8188eu: irq_prepare_beacon_tasklet is unused

irq_prepare_beacon_tasklet in struct recv_priv is not used for r8188eu.
Remove it.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20220226181457.1138035-3-martin@kaiser.cx


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>