mfd: da9062-core: Rename get_device_type to da9062_get_device_type

Rename get_device_type() to da9062_get_device_type().
This function is only used in this file so make it static.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>