OMAPDSS: HDMI5: Fix AVI infoframe

The AVI infoframe R0-R3 in the 2nd data byte represents the
Active Format Aspect Ratio. It is four bits long not two bits.
This fixes that mask used to extract the bits before writing the
bits to the hardware registers.

Signed-off-by: Jim Lodes <jim.lodes@garmin.com>
Signed-off-by: J.D. Schroeder <jay.schroeder@garmin.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>