mux: adgs1408: fix Wvoid-pointer-to-enum-cast warning

mux: adgs1408: fix Wvoid-pointer-to-enum-cast warning

'chip_id' is an enum, thus cast of pointer on 64-bit compile test with
W=1 causes:

  adgs1408.c:63:12: error: cast to smaller integer type 'enum adgs1408_chip_id' from 'const void *' [-Werror,-Wvoid-pointer-to-enum-cast]

Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20250501181819.164207-2-krzysztof.kozlowski@linaro.org
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>