drivers/base/devtmpfs.c: correct annotation of `setup_done'

This fixes the following section mismatch issue:

WARNING: vmlinux.o(.text+0x1192bf): Section mismatch in reference from the function devtmpfsd() to the variable .init.data:setup_done
The function devtmpfsd() references the variable __initdata setup_done.
This is often because devtmpfsd lacks a __initdata annotation or the annotation of setup_done is wrong.

WARNING: vmlinux.o(.text+0x119342): Section mismatch in reference from the function devtmpfsd() to the variable .init.data:setup_done
The function devtmpfsd() references the variable __initdata setup_done.
This is often because devtmpfsd lacks a __initdata annotation or the annotation of setup_done is wrong.

Signed-off-by: Arnaud Lacombe <lacombar@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>