i2c: mux: remove incorrect of_match_ptr annotations

Building with W=1 shows a warning about ltc4306_of_match and
i2c_mux_reg_of_match being unused when CONFIG_OF is disabled:

    drivers/i2c/muxes/i2c-mux-ltc4306.c:200:34: error: unused variable 'ltc4306_of_match' [-Werror,-Wunused-const-variable]
    drivers/i2c/muxes/i2c-mux-reg.c:242:34: error: unused variable 'i2c_mux_reg_of_match' [-Werror,-Wunused-const-variable]

Acked-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>
Link: https://lore.kernel.org/r/20250225163700.4169480-1-arnd@kernel.org