usb: musb: host: correct cppi dma channel for isoch transfer

Incorrect cppi dma channel is referenced in musb_rx_dma_iso_cppi41(),
which causes kernel NULL pointer reference oops later when calling
cppi41_dma_channel_program().

Fixes: 069a3fd1 (usb: musb: Remove ifdefs for musb_host_rx in musb_host.c
part1)

Cc: <stable@vger.kernel.org> # v4.2+
Reported-by: Matwey V. Kornilov <matwey@sai.msu.ru>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Bin Liu <b-liu@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>