s390/mem_detect: add missing include

Fix this allnoconfig build breakage:

arch/s390/boot/mem_detect.c: In function 'tprot':
arch/s390/boot/mem_detect.c:122:12: error: 'EFAULT' undeclared (first use in this function)
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/boot/mem_detect.c

 // SPDX-License-Identifier: GPL-2.0
+#include <linux/errno.h>
 #include <linux/init.h>
 #include <asm/sclp.h>
 #include <asm/sections.h>