kconfig: Delete unnecessary checks before the function call "sym_calc_value"

The sym_calc_value() function tests whether its argument is NULL and then
returns immediately. Thus the test around the call is not needed.

This issue was detected by using the Coccinelle software.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: Michal Marek <mmarek@suse.com>
Signed-off-by: Christian Lamparter <chunkeey@googlemail.com>