arch: um: kmsg_dump: Use console_is_usable

All consoles found on for_each_console are registered, meaning that all
of them have the CON_ENABLED flag set. Since NBCON was introduced it's
important to check if a given console also implements the NBCON callbacks.
The function console_is_usable does exactly that.

Signed-off-by: Marcos Paulo de Souza <[e-mail]>
Reviewed-by: Petr Mladek <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Petr Mladek <[e-mail]>

arch/um/kernel/kmsg_dump.c

···
 		 * expected to output the crash information.
 		 */
 		if (strcmp(con->name, "ttynull") != 0 &&
-		    (console_srcu_read_flags(con) & CON_ENABLED)) {
+		    console_is_usable(con, console_srcu_read_flags(con), true)) {
 			break;
 		}
 	}