mmc: meson-mx-sdio: return correct error code

This has a copy and paste bug so we use "host->fixed_factor_clk" which
is a valid pointer instead of "host->cfg_div_clk" which holds the error
code.

Fixes: ed80a13b ("mmc: meson-mx-sdio: Add a driver for the Amlogic Meson8 and Meson8b SoCs")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>