mmc: atmel-mci: don't use dma features when using DMA with no chan available

commit ef8781989a1bcd05aa47e853917c37df44917194 upstream.

Some callbacks are set too early -- i.e. we can have dma capabilities but
we can't get a dma channel. So wait to get the dma channel before setting
callbacks and change logs consequently.

Signed-off-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Chris Ball <cjb@laptop.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>