s390/sclp: fix compile error

Fix this error when compiling with CONFIG_SMP=n and
CONFIG_DYNAMIC_DEBUG=y:

drivers/s390/char/sclp_early.c: In function 'sclp_read_info_early':
drivers/s390/char/sclp_early.c:87:19: error: 'EBUSY' undeclared (first use in this function)
   } while (rc == -EBUSY);
                   ^

Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>