viafb: fix LCD hardware cursor regression

Although I'd consider this a hardware bug, as there is hardware out that
for whatever reason does not support hardware cursors on LCD output we
have to care about it in the driver.  This fixes a regression (invisible
cursor) introduced by:

    viafb: cleanup viafb_cursor

Signed-off-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>
Reported-by: Julian Wollrath <jwollrath@web.de>
Tested-by: Julian Wollrath <jwollrath@web.de>
Cc: Scott Fang <ScottFang@viatech.com.cn>
Cc: Joseph Chan <JosephChan@via.com.tw>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>