[media] dib7000m: Remove unnecessary null test

This patch removes the null test on ch. ch is initialized at the
beginning of the function to &demod->dtv_property_cache. Since demod
is dereferenced prior to the null test, demod must be a valid pointer,
and &demod->dtv_property_cache cannot be null.

The following Coccinelle script is used for detecting the change:

@r@
expression e,f;
identifier g,y;
statement S1,S2;
@@

*e = &f->g
<+...
 f->y
 ...+>
*if (e != NULL || ...)
 S1 else S2

Signed-off-by: Himangi Saraogi <himangi774@gmail.com>
Acked-by: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>