util/tgsi: use ASSERT_BITFIELD_SIZE() to check opcode field size

I've noticed at least two places where we store the TGSI opcode in
an unsigned:8 bitfield.  We're at 249 opcodes now.  If we hit 256 we'll
need to grow those bitfields.  Use the new ASSERT_BITFIELD_SIZE() macro
to detect that.

Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>

src/gallium/auxiliary/tgsi/tgsi_info.c

@@ -55,6 +55,8 @@ tgsi_get_opcode_info( uint opcode )
 {
    static boolean firsttime = 1;
 
+   ASSERT_BITFIELD_SIZE(struct tgsi_opcode_info, opcode, TGSI_OPCODE_LAST - 1);
+
    if (firsttime) {
       unsigned i;
       firsttime = 0;