x86: Silence GCC 12 warning on tc-i386.c

Silence GCC 12 warning on tc-i386.c:

gas/config/tc-i386.c: In function ‘md_assemble’:
gas/config/tc-i386.c:5039:16: error: too many arguments for format [-Werror=format-extra-args]
 5039 |     as_warn (_("only support RIP-relative address"), i.tm.name);

	* config/tc-i386.c (md_assemble): Print mnemonic in RIP-relative
	warning.
	* estsuite/gas/i386/x86-64-prefetchi-warn.l: Updated.