mdacon: replace MDA_ADDR macro by inline function

MDA_ADDR is one of those macros which could be an inline function. So
convert MDA_ADDR to mda_addr.

Note that we take x and y as unsigned now. But they are absolute
coordinates, so this is no problem.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>