mfd: palmas: Remove call of mfd_remove_devices

The driver only support the device tree and sub modules are populated
through platform, the registration of sub devices through mfd_add_devices
has been removed.

Hence in remove path of the driver, it is not require to call
mfd_remove_devices.

Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>