extcon: max77693: add device-tree compatible string

Commit 57f706bf

 ("ARM: dts: samsung: exynos4412-midas: add USB
connector and USB OTG") added a 'muic' node to the MAX77693 PMIC
definition in various device-tree files. Since that commit, the newly
created MFD cell gained its own of_node and compatible string. This
changed its modalias, what in turn broke automated loading of the driver
module, because the new modalias is based on the of_node compatible
string, not the platform device name.

Fix this by adding the needed device-tree compatible string.

Link: https://lore.kernel.org/all/20231006100434.2908243-1-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>