OMAP: DSS2: Ensure non-zero FIR values are configured

OMAP: DSS2: Ensure non-zero FIR values are configured

FIR values can never be zero as per TRM, and the current code writes zero
when scaling is not used. It was not causing any problem as scaling was
disabled when zero was written. Its still safer to not write zero to
it in any case.
Now we configure correct FIR values even when scaling is not used (i.e. set FIR
to 1024 when scaling is not used), but the scaling enable bits are still kept
off if the scaling is not needed.

Signed-off-by: Amber Jain <amber@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>