[S390] Fix linker script.

Fixes this warning:
vmlinux: warning: allocated section `.text' not in segment
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kernel/vmlinux.lds.S

@@ -35,7 +35,7 @@ SECTIONS
 		KPROBES_TEXT
 		*(.fixup)
 		*(.gnu.warning)
-	} = 0x0700
+	} :text = 0x0700
 
 	_etext = .;		/* End of text section */