regulator: aat2870: Fix the logic of checking if no id is matched in aat2870_get_regulator

In current implementation, the pointer ri is not NULL if no id is matched.
Fix it by checking i == ARRAY_SIZE(aat2870_regulators) if no id is matched.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Cc: stable@kernel.org