power: supply: sbs-manager: Remove class argument from i2c_mux_add_adapter()

Commit 99a741aa7a2d ("i2c: mux: gpio: remove support for class-based
device instantiation") removed the last call to i2c_mux_add_adapter()
with a non-null class argument. Therefore the class argument can be
removed.

Note: Class-based device instantiation is a legacy mechanism which
shouldn't be used in new code, so we can rule out that this argument
may be needed again in the future.

This driver was forgotten by the patch in the Fixes tag.

Fixes: fec1982d ("i2c: mux: Remove class argument from i2c_mux_add_adapter()")
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Acked-by: Sebastian Reichel <sebastian.reichel@collabora.com>