firmware: cs_dsp: Append \n to debugfs string during read

firmware: cs_dsp: Append \n to debugfs string during read

Append the terminating \n to the string during the debugfs file
read instead of creating a string that already has a trailing \n.

This avoids the ugly behaviour of having to include a trailing \n
in the filenames stored to wmfw_file_name and bin_file_name in
struct cs_dsp.

Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Link: https://patch.msgid.link/20251120130640.1169780-3-rf@opensource.cirrus.com
Signed-off-by: Mark Brown <broonie@kernel.org>