intel/vulkan: assume() that we don't use "ISL_NUM_FORMATS"

Which coverity thinks will happen, even though we never return
ISL_NUM_FORMATS.

CID: 1559463
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/27369>

src/intel/vulkan/genX_pipeline.c

@@ -185,6 +185,7 @@ genX(emit_vertex_input)(struct anv_batch *batch,
                                                   vi->attributes[a].format,
                                                   VK_IMAGE_ASPECT_COLOR_BIT,
                                                   VK_IMAGE_TILING_LINEAR);
+      assume(format < ISL_NUM_FORMATS);
 
       uint32_t binding = vi->attributes[a].binding;
       assert(binding < MAX_VBS);