disas/nanomips: Move setjmp into nanomips_dis

disas/nanomips: Move setjmp into nanomips_dis

Reduce the number of local variables within the scope of the
setjmp by moving it to the existing helper.  The actual length
returned from Disassemble is not used, because we have already
determined the length while reading bytes.  Fixes:

nanomips.c: In function ‘print_insn_nanomips’:
nanomips.c:21925:14: error: variable ‘insn1’ might be clobbered by ‘longjmp’ or ‘vfork’ [-Werror=clobbered]
nanomips.c:21925:25: error: variable ‘insn2’ might be clobbered by ‘longjmp’ or ‘vfork’ [-Werror=clobbered]
nanomips.c:21925:36: error: variable ‘insn3’ might be clobbered by ‘longjmp’ or ‘vfork’ [-Werror=clobbered]
nanomips.c:21926:22: error: variable ‘buf’ might be clobbered by ‘longjmp’ or ‘vfork’ [-Werror=clobbered]

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20221106212852.152384-2-richard.henderson@linaro.org>