Bluetooth: shell: Log failure to register authentication handlers

Log failure to register authentication handlers since returning errors
from the shell is not visible to the user.

Signed-off-by: Joakim Andersson <joakim.andersson@nordicsemi.no>

subsys/bluetooth/shell/bt.c

@@ -2841,6 +2841,10 @@ static int cmd_auth(const struct shell *sh, size_t argc, char *argv[])
 		return SHELL_CMD_HELP_PRINTED;
 	}
 
+	if (err) {
+		shell_error(sh, "Failed to set auth handlers (%d)", err);
+	}
+
 	return err;
 }