firmware: cs_dsp: Make wmfw and bin filename arguments const char *

The wmfw_filename and bin_filename strings passed into cs_dsp_power_up()
and cs_dsp_adsp1_power_up() should be const char *.

Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Reviewed-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Link: https://lore.kernel.org/r/20240710103640.78197-3-rf@opensource.cirrus.com
Signed-off-by: Mark Brown <broonie@kernel.org>