mfd: kempld-core: Fix callback return value check

[ Upstream commit c8648508ebfc597058d2cd00b6c539110264a167 ]

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

Cc: stable@vger.kernel.org
Signed-off-by: Ameya Palande <2ameya@gmail.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>