iommu/omap: Use int type to store negative error codes

iommu/omap: Use int type to store negative error codes

Change the 'ret' variable from u32 to int to store negative error codes
or zero;

Storing the negative error codes in unsigned type, doesn't cause an issue
at runtime but it's ugly. 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: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/20250829140219.121783-1-rongqianfeng@vivo.com
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>