simplify checks for I_CLEAR/I_FREEING

add I_CLEAR instead of replacing I_FREEING with it.  I_CLEAR is
equivalent to I_FREEING for almost all code looking at either;
it's there to keep track of having called clear_inode() exactly
once per inode lifetime, at some point after having set I_FREEING.
I_CLEAR and I_FREEING never get set at the same time with the
current code, so we can switch to setting i_flags to I_FREEING | I_CLEAR
instead of I_CLEAR without loss of information.  As the result of
such change, checks become simpler and the amount of code that needs
to know about I_CLEAR shrinks a lot.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/nilfs2/gcdat.c b/fs/nilfs2/gcdat.c
index dd5f7e0..84a45d1 100644
--- a/fs/nilfs2/gcdat.c
+++ b/fs/nilfs2/gcdat.c
@@ -78,7 +78,7 @@
 	struct inode *gcdat = nilfs->ns_gc_dat;
 	struct nilfs_inode_info *gii = NILFS_I(gcdat);
 
-	gcdat->i_state = I_CLEAR;
+	gcdat->i_state = I_FREEING | I_CLEAR;
 	gii->i_flags = 0;
 
 	nilfs_palloc_clear_cache(gcdat);