drivers/video/w100fb.c: ignore void return value / fix build failure

Fix a build failure "error: void value not ignored as it ought to be"
by removing an assignment of a void return value.  The functionality of
the code is not changed.

Signed-off-by: Peter Huewe <peterhuewe@gmx.de>
Acked-by: Henrik Kretzschmar <henne@nachtwindheim.de>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>