Staging: vt6656: Remove explicit comparisons against NULL

Explicit comparisons of pointers agains NULL
(like if (p != NULL) ...) are not as readable as the implicit
comparison (like if (p) ...). This patch converts all these explicit
comparisons to implicit ones.

Signed-off-by: Sebastian Rachuj <sebastian.rachuj@studium.uni-erlangen.de>
Signed-off-by: Simon Schuster <linux@rationality.eu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>