gpu: host1x: Use a signed return type for do_relocs()

The return type "unsigned int" was used by the do_relocs() function
despite the fact that it will eventually return a negative error code.
Use a signed integer instead to accomodate for error codes.

This issue was detected by using the Coccinelle software.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: Thierry Reding <treding@nvidia.com>