kernel: modules: fix mlxreg dependency to avoid deferred probe

kernel: modules: fix mlxreg dependency to avoid deferred probe

The mlxreg-hotplug platform driver was failing to probe due to a missing
I²C multiplexer dependency. Previously, only kmod-i2c-mux-mlxcpld was
declared, but mlxreg also requires kmod-i2c-mux-reg to initialize its
I²C mux functionality.

Without this dependency, the driver probe was deferred:

  [   24.902331] platform mlxreg-hotplug: deferred probe pending: (reason unknown)

With kmod-i2c-mux-reg added, the probe succeeds and the expected
multiplexed I²C buses are registered:

  [   15.793884] i2c i2c-1: Added multiplexed i2c bus 2
  [   15.799391] i2c i2c-1: Added multiplexed i2c bus 3
  [   15.804830] i2c i2c-1: Added multiplexed i2c bus 4
  ...

Signed-off-by: Til Kaiser <mail@tk154.de>
Link: https://github.com/openwrt/openwrt/pull/20274
Signed-off-by: Robert Marko <robimarko@gmail.com>