x86: linker script syntax nits

The linker scripts grew some use of weirdly wrong linker script syntax.
It happens to work, but it's not what the syntax is documented to be.
Clean it up to use the official syntax.

Signed-off-by: Roland McGrath <roland@redhat.com>
CC: Ian Lance Taylor <iant@google.com>

arch/x86/kernel/acpi/realmode/wakeup.lds.S

@@ -56,6 +56,6 @@ SECTIONS
 	/DISCARD/ : {
 		*(.note*)
 	}
-
-	. = ASSERT(_end <= WAKEUP_SIZE, "Wakeup too big!");
 }
+
+ASSERT(_end <= WAKEUP_SIZE, "Wakeup too big!");