ocfs2: Handle value tree roots in ocfs2_xa_set_inline_value()

Previously the xattr code would send in a fake value, containing a tree
root, to the function that installed name+value pairs.  Instead, we pass
the real value to ocfs2_xa_set_inline_value(), and it notices that the
value cannot fit.  Thus, it installs a tree root.

Signed-off-by: Joel Becker <joel.becker@oracle.com>