staging: r8188eu: remove code to get int in pipe handle

After the previous cleanup, ffaddr2pipehdl is called only by
rtw_write_port. This function will never ask for the pipe handle
of the interrupt in pipe. We can remove the related code.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20211126173205.21352-5-martin@kaiser.cx


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