intel: Fix release-build warnings about sf_entry_size.

In one side of the ifdef it's only used in an assert.

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5829>
diff --git a/src/intel/blorp/blorp_genX_exec.h b/src/intel/blorp/blorp_genX_exec.h
index 48b1634..a8e5edd 100644
--- a/src/intel/blorp/blorp_genX_exec.h
+++ b/src/intel/blorp/blorp_genX_exec.h
@@ -209,7 +209,7 @@
    /* The URB size is expressed in units of 64 bytes (512 bits) */
    const unsigned vs_entry_size = DIV_ROUND_UP(total_needed, 64);
 
-   const unsigned sf_entry_size =
+   ASSERTED const unsigned sf_entry_size =
       params->sf_prog_data ? params->sf_prog_data->urb_entry_size : 0;
 
 #if GEN_GEN >= 7