Fix xtensa "clobbered by longjmp" warnings

Fix xtensa "clobbered by longjmp" warnings

.../opcodes/xtensa-dis.c: In function ‘print_insn_xtensa’:
.../opcodes/xtensa-dis.c:257:17: error: variable ‘fmt’ might be clobbered by ‘longjmp’ or ‘vfork’ [-Werror=clobbered]
   xtensa_format fmt;
                 ^~~
.../opcodes/xtensa-dis.c:262:26: error: variable ‘valid_insn’ might be clobbered by ‘longjmp’ or ‘vfork’ [-Werror=clobbered]
   int first, first_slot, valid_insn = 0;
                          ^~~~~~~~~~

	* xtensa-dis.c (print_insn_xtensa): Init fmt and valid_insn after
	setjmp.  Move init for some other vars later too.