disp: msm: dsi: Clear slave dma status only for broadcast command

In case of broadcast, for master controller, DMA_DONE bit gets
cleared in dsi_ctrl_isr and for slave controller it gets cleared
in clear_slave_dma_status. Current implementation checks
DSI_CTRL_CMD_BROADCAST_MASTER flag to decide if it's slave or not.
But, in the case of unicast, this flag is not set, leading to
the unnecessary poll for clear_slave_dma_status for all unicast
command transfers.

Add a check to call clear_slave_dma_status only when the current
command is broadcast on slave controller.

Change-Id: I7156f8c12ec779b41dafc8fc67639814957ee51b
Signed-off-by: Rajeev Nandan <quic_rajeevny@quicinc.com>