s390/test_unwind: fix spelling mistake "reqister" -> "register"

There is a spelling mistake in a pr_info message. Fix it.

Link: https://lkml.kernel.org/r/20191202090215.28766-1-colin.king@canonical.com
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

arch/s390/lib/test_unwind.c

@@ -238,7 +238,7 @@ static int test_unwind_irq(struct unwindme *u)
 {
 	preempt_disable();
 	if (register_external_irq(EXT_IRQ_CLK_COMP, unwindme_irq_handler)) {
-		pr_info("Couldn't reqister external interrupt handler");
+		pr_info("Couldn't register external interrupt handler");
 		return -1;
 	}
 	u->task = current;