x86/boot/compressed/sev-es: Convert to insn_decode()

Other than simplifying the code there should be no functional changes
resulting from this.
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20210304174237.31945-7-bp@alien8.de

arch/x86/boot/compressed/sev-es.c

@@ -78,16 +78,15 @@ static inline void sev_es_wr_ghcb_msr(u64 val)
 static enum es_result vc_decode_insn(struct es_em_ctxt *ctxt)
 {
 	char buffer[MAX_INSN_SIZE];
-	enum es_result ret;
+	int ret;
 
 	memcpy(buffer, (unsigned char *)ctxt->regs->ip, MAX_INSN_SIZE);
 
-	insn_init(&ctxt->insn, buffer, MAX_INSN_SIZE, 1);
-	insn_get_length(&ctxt->insn);
+	ret = insn_decode(&ctxt->insn, buffer, MAX_INSN_SIZE, INSN_MODE_64);
+	if (ret < 0)
+		return ES_DECODE_FAILED;
 
-	ret = ctxt->insn.immediate.got ? ES_OK : ES_DECODE_FAILED;
-
-	return ret;
+	return ES_OK;
 }
 
 static enum es_result vc_write_mem(struct es_em_ctxt *ctxt,