s390/sclp: fix declaration of _sclp_print_early()

_sclp_print_early() has return value: at present, return 0 for OK, 1 for
failure. It returns '%r2', so use 'long' as return value (upper caller
can check '%r2' directly). The related warning:

    CC      arch/s390/boot/compressed/misc.o
  arch/s390/boot/compressed/misc.c:66:8: warning: type defaults to 'int' in declaration of '_sclp_print_early' [-Wimplicit-int]
   extern _sclp_print_early(const char *);
          ^

At present, _sclp_print_early() is only used by puts(), so can still
remain its declaration in 'misc.c' file.

[heiko.carstens@de.ibm.com]: move declaration to sclp.h header file
Signed-off-by: NChen Gang <gang.chen.5i5j@gmail.com>
Signed-off-by: NHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/boot/compressed/misc.c

@@ -8,6 +8,7 @@
 
 #include <asm/uaccess.h>
 #include <asm/page.h>
+#include <asm/sclp.h>
 #include <asm/ipl.h>
 #include "sizes.h"
 
@@ -63,8 +64,6 @@ static unsigned long free_mem_end_ptr;
 #include "../../../../lib/decompress_unxz.c"
 #endif
 
-extern _sclp_print_early(const char *);
-
 static int puts(const char *s)
 {
 	_sclp_print_early(s);

arch/s390/include/asm/sclp.h

@@ -68,4 +68,6 @@ void sclp_early_detect(void);
 int sclp_has_siif(void);
 unsigned int sclp_get_ibc(void);
 
+long _sclp_print_early(const char *);
+
 #endif /* _ASM_S390_SCLP_H */