video: fbdev: bt431: Correct cursor format control macro

The Bt431 cursor generator supports simultaneous generation of a 64 x 64
and a cross hair cursor in which the cursor format control bit (bit D4)
of the command register "specifies whether the contents of the cursor
RAM are to be logically exclusive-ORed (logical zero) or ORed (logical
one) with the cross hair cursor".  Rename the relevant macro accordingly.

References:

[1] "Bt431 Monolithic CMOS 64 x 64 Pixel Cursor Generator", Brooktree
    Corporation, Document Number: L431001, Rev. J

Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>