mfd: Kconfig: Rename Samsung to lowercase

Fix up inconsistent usage of upper and lowercase letters in "Samsung"
name.

"SAMSUNG" is not an abbreviation but a regular trademarked name.
Therefore it should be written with lowercase letters starting with
capital letter.

Although advertisement materials usually use uppercase "SAMSUNG", the
lowercase version is used in all legal aspects (e.g. on Wikipedia and in
privacy/legal statements on
https://www.samsung.com/semiconductor/privacy-global/

).

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>