x86/insn: Directly assign x86_64 state in insn_init()

No point in checking again as this was already done by the caller.

Signed-off-by: Nikolay Borisov <nik.borisov@suse.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20240222111636.2214523-3-nik.borisov@suse.com