On probe error the driver should free the memory allocated for private
structure.  Fix this by using resource-managed allocation.

Fixes: a20cbdef ("powerpc/fsl: Add support for Integrated Flash Controller")
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Link: https://lore.kernel.org/r/20210527154322.81253-2-krzysztof.kozlowski@canonical.com