mfd: kempld-core: Fix callback return value check

commit c8648508 upstream.

On success, callback function returns 0. So invert the if condition
check so that we can break out of loop.

Signed-off-by: Ameya Palande <2ameya@gmail.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>