x86: fix CMPXCHG8B special case when disallowing q suffix outside of 64-bit mode

[Jan Beulich]

In match_template() i.tm hasn't been filled yet, so it is necessarily t
which needs checking. This is only a latent issue as no other templates
with the same base_opcode have an extension_opcode of 1.

gas/
2021-03-XX  Jan Beulich  <jbeulich@suse.com>

	* config/tc-i386.c (match_template): Use t instead of i.tm.

--- a/gas/config/tc-i386.c
+++ b/gas/config/tc-i386.c
@@ -6290,7 +6290,7 @@ match_template (char mnem_suffix)
       if (((i.suffix == QWORD_MNEM_SUFFIX
 	    && flag_code != CODE_64BIT
 	    && !(t->base_opcode == 0xfc7
-		 && i.tm.opcode_modifier.opcodeprefix == PREFIX_NONE
+		 && t->opcode_modifier.opcodeprefix == PREFIX_NONE
 		 && t->extension_opcode == 1) /* cmpxchg8b */)
 	   || (i.suffix == LONG_MNEM_SUFFIX
 	       && !cpu_arch_flags.bitfield.cpui386))