macintosh: Fix warning comparing pointer to 0

Fix the following coccicheck warnings:
./drivers/macintosh/via-cuda.c:240:16-17: WARNING comparing pointer to 0
./drivers/macintosh/via-cuda.c:243:16-17: WARNING comparing pointer to
0, suggest !E
./drivers/macintosh/via-cuda.c:521:23-24: WARNING comparing pointer to 0

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220214010558.130201-1-yang.lee@linux.alibaba.com