image-fit: Fix compiler warning in fit_conf_print()

This fixes the following compiler warning:

In file included from tools/common/image-fit.c:1:0:
./tools/../common/image-fit.c: In function ‘fit_conf_print’:
./tools/../common/image-fit.c:1470:27: warning: logical not is only applied
 to the left hand side of comparison [-Wlogical-not-parentheses]
    (const char **)&uname) > 0;

Signed-off-by: Hans de Goede <hdegoede@redhat.com>