drivers/video/w100fb.c: avoid a couple of error-path NULL derefs

Fix a couple of error-patch oopses identified by Marcio Buss in
http://bugzilla.kernel.org/show_bug.cgi?id=9567

.

Cc: Marcio Buss <marciobuss@gmail.com>
Cc: Jeff Zhou <xinzhou.sjtu@gmail.com>
Cc: "Antonino A. Daplas" <adaplas@pol.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>