firmware: cs_dsp: Fix overrun of unterminated control name string

firmware: cs_dsp: Fix overrun of unterminated control name string

For wmfw format v2 and later the coefficient name strings have a length
field and are NOT null-terminated. Use kasprintf() to convert the
unterminated string into a null-terminated string in an allocated buffer.

The previous code handled this duplication incorrectly using kmemdup()
and getting the length from a strlen() of the (unterminated) source string.
This resulted in creating a string that continued up to the next byte in
the firmware file that just happened to be 0x00.

Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Fixes: bfb815d7099e ("firmware: cs_dsp: add driver to support firmware loading on Cirrus Logic DSPs")
Link: https://lore.kernel.org/r/20220412163927.1303470-1-rf@opensource.cirrus.com
Signed-off-by: Mark Brown <broonie@kernel.org>