i2c: mux: mlxcpld: Extend supported mux number

Allow to extend mux number supported by driver.
Currently it is limited by eight, which is not enough for new coming
Mellanox modular system with line cards, which require up to 64 mux
support.

Signed-off-by: Vadim Pasternak <vadimp@nvidia.com>
Reviewed-by: Michael Shych <michaelsh@nvidia.com>
Acked-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Wolfram Sang <wsa@kernel.org>