sw/vec_iree: fix run-time error in some GCC compiled targets

This change avoids runtime errors in targets like blc_test in kelvin GCC
compilation.

Change-Id: I790e4ef5764ce527a6d04cd6906854371c9865dc

risp4ml/common/test_utils.h

diff --git a/risp4ml/common/test_utils.h b/risp4ml/common/test_utils.h
index 68978f7..a7053af 100644
--- a/risp4ml/common/test_utils.h
+++ b/risp4ml/common/test_utils.h
@@ -39,7 +39,7 @@
 // Initializes raw image to random value within min and max range
 static inline void InitImageRandom(Image* image, pixel_type_t min_val,
                                    pixel_type_t max_val) {
-  pixel_type_t range = max_val + 1 - min_val;
+  int range = max_val + 1 - min_val;
   for (uint16_t c = 0; c < image->num_channels; ++c) {
     for (uint16_t y = 0; y < image->height; ++y) {
       for (uint16_t x = 0; x < image->width; ++x) {