msm: mdss: Add error check for cmds_tx and cmds_rx APIs

Currently in the MDSS DSI driver, there is no error checking
and return for add, dma_tx and dma_rx functions in cmds_tx
and cmds_rx APIs in case read or write operations fails.
So, added error checks and return messages. Also, enable
irq after dma_add in cmds_rx in correspondence with cmdx_tx api.

Change-Id: I0fc2310ae8476510b3f903382988fec25cc2efdb
Signed-off-by: Jayant Shekhar <jshekhar@codeaurora.org>