Print width and height as %ux%u instead of %u/%u

src/read.c

diff --git a/src/read.c b/src/read.c
index d363f84..bd4c3b3 100644
--- a/src/read.c
+++ b/src/read.c
@@ -950,7 +950,7 @@
 
     if (tilesRequested != tilesAvailable) {
         avifDiagnosticsPrintf(data->diag,
-                              "Grid image of dimensions %u/%u requires %u tiles, and only %u were found",
+                              "Grid image of dimensions %ux%u requires %u tiles, and only %u were found",
                               grid->columns,
                               grid->rows,
                               tilesRequested,
@@ -1045,7 +1045,7 @@
     // The tile_width shall be greater than or equal to 64, and the tile_height shall be greater than or equal to 64.
     if ((firstTile->image->width < 64) || (firstTile->image->height < 64)) {
         avifDiagnosticsPrintf(data->diag,
-                              "Grid image tiles are smaller than 64x64 (%u/%u). See MIAF (ISO/IEC 23000-22:2019), Section 7.3.11.4.2",
+                              "Grid image tiles are smaller than 64x64 (%ux%u). See MIAF (ISO/IEC 23000-22:2019), Section 7.3.11.4.2",
                               firstTile->image->width,
                               firstTile->image->height);
         return AVIF_FALSE;