mesa: Fix packing of stencil bits to MESA_FORMAT_Z32_FLOAT_X24S8.

We were converting our ubyte stencil value to a float.  Just write it
as a uint, which overwrites the X24 part of X24S8 with 0 but shouldn't
matter.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Brian Paul <brianp@vmware.com>

src/mesa/main/format_pack.c

@@ -2453,7 +2453,7 @@ _mesa_pack_ubyte_stencil_row(gl_format format, GLuint n,
       break;
    case MESA_FORMAT_Z32_FLOAT_X24S8:
       {
-         GLfloat *d = ((GLfloat *) dst);
+         GLuint *d = dst;
          GLuint i;
          for (i = 0; i < n; i++) {
             d[i * 2 + 1] = src[i];