x86/alternative: Use insn_decode()

No functional changes, just simplification.
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20210304174237.31945-10-bp@alien8.de

arch/x86/kernel/alternative.c

@@ -1274,15 +1274,15 @@ static void text_poke_loc_init(struct text_poke_loc *tp, void *addr,
 			       const void *opcode, size_t len, const void *emulate)
 {
 	struct insn insn;
+	int ret;
 
 	memcpy((void *)tp->text, opcode, len);
 	if (!emulate)
 		emulate = opcode;
 
-	kernel_insn_init(&insn, emulate, MAX_INSN_SIZE);
-	insn_get_length(&insn);
+	ret = insn_decode(&insn, emulate, MAX_INSN_SIZE, INSN_MODE_KERN);
 
-	BUG_ON(!insn_complete(&insn));
+	BUG_ON(ret < 0);
 	BUG_ON(len != insn.length);
 
 	tp->rel_addr = addr - (void *)_stext;