video: mmpfb: cleanup some static checker warnings in probe()

Sparse complains about using zero instead of NULL for pointers.
Probably, if we enabled the warning, then GCC would complain about the
unused initializers.  I've just removed them.

Smatch complains that we first check if "fbi" is NULL and then
dereference it in the error handling.  It turns out that "fbi" can't be
NULL so I've removed the check.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>