regulator: scmi: Use int type to store negative error codes

Change the 'ret' variable from u32 to int to store negative error codes or
zero returned by of_property_read_u32().

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: Sudeep Holla <sudeep.holla@arm.com>
Fixes: 0fbeae70 ("regulator: add SCMI driver")
Link: https://patch.msgid.link/20250829101411.625214-1-rongqianfeng@vivo.com


Signed-off-by: Mark Brown <broonie@kernel.org>