NAND: davinci: Fix warnings when 4-bit ECC not used

I accidentally left v2 of "NAND: DaVinci:Adding 4 BIT ECC support"
applied when I pushed the tree last merge window, and missed these fixes
which were in v3 of that patch.

Signed-off-by: Sandeep Paulraj <s-paulraj@ti.com>
Signed-off-by: Scott Wood <scottwood@freescale.com>