clk: meson: gxbb: remove IGNORE_UNUSED from mmc clocks

Remove CLK_IGNORE_UNUSED from mmc clocks. This was only needed while the
mmc driver incorrectly used the xtal as source instead of the mmc
clock. Now, the driver takes the correct clock, CCF is aware that the
clock is being used and we can remove this flag.

Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Acked-by: Kevin Hilman <khilman@baylibre.com>