libpisp: backend_debug: Use unsigned int

The mainline version of pisp_be_config.h header defines the
'num_tiles' member of 'struct pisp_be_tiles_config' as an unsigned
32-bit value.

Use an unsigned integer as loop variable to avoid the following
compilation error:

error: comparison of integer expressions of different signedness

Signed-off-by: Jacopo Mondi <[email protected]>

src/libpisp/backend/backend_debug.cpp

@@ -501,7 +501,7 @@ std::string BackEnd::GetJsonConfig(pisp_be_tiles_config *config)
 		j["config"].push_back(b);
 	}
 
-	for (int t = 0; t < config->num_tiles; t++)
+	for (unsigned int t = 0; t < config->num_tiles; t++)
 	{
 		json b;
 		for (auto const &field : tiles_config.fields)