extcon: max77843: add device-tree compatible string

Add the needed device-tree compatible string to the MAX77843 extcon
driver, so it can be automatically loaded when compiled as a kernel
module and given device-tree contains separate 'muic' node under the main
MAX77843 PMIC node.

Link: https://lore.kernel.org/all/20231006100434.2908243-2-m.szyprowski@samsung.com/
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>