ASoC: adau1977: use int type to store negative error codes

Change the 'ret' variable from unsigned int to int to store negative error
codes or zero returned by regmap_update_bits().

Storing the negative error codes in unsigned type, doesn't cause an issue
at runtime but it's ugly as pants. Additionally, assigning negative error
codes to unsigned type may trigger a GCC warning when the -Wsign-conversion
flag is enabled.

No effect on runtime.

Signed-off-by: Qianfeng Rong <rongqianfeng@vivo.com>
Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Message-ID: <20250828075406.386208-3-rongqianfeng@vivo.com>
Signed-off-by: Mark Brown <broonie@kernel.org>