arm64: fix return code check when changing emulation handler

update_insn_emulation_mode() returns 0 on success, so we should be
treating any non-zero values as failure, rather than the other way
around. Otherwise, writes to the sysctl file controlling the emulation
are ignored and immediately rolled back.
Reported-by: Gene Hackmann <ghackmann@google.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/kernel/armv8_deprecated.c

@@ -165,7 +165,7 @@ static int emulation_proc_handler(struct ctl_table *table, int write,
 		goto ret;
 
 	ret = update_insn_emulation_mode(insn, prev_mode);
-	if (!ret) {
+	if (ret) {
 		/* Mode change failed, revert to previous mode. */
 		insn->current_mode = prev_mode;
 		update_insn_emulation_mode(insn, INSN_UNDEF);