ASoC: tas2781: bound firmware description string parsing

ASoC: tas2781: bound firmware description string parsing

The TAS2781 firmware parser reads several variable-length description
strings with strlen() before checking that the string terminator is
present inside the firmware blob. A malformed firmware image without a
NUL terminator can therefore make the parser walk past the end of the
firmware buffer before the later size checks run.

Add a small bounded string-length helper and use it for all description
fields that are parsed from the firmware buffer. Keep the existing size
checks for the fixed bytes that follow each string.

Fixes: 915f5eadebd2 ("ASoC: tas2781: firmware lib")
Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn>
Link: https://patch.msgid.link/20260706144540.93929-1-pengpeng@iscas.ac.cn
Signed-off-by: Mark Brown <broonie@kernel.org>