ocfs2: Use ocfs2_xattr_value_buf in ocfs2_xattr_set_entry().

ocfs2_xattr_set_entry is the function that knows what type of block it
is setting into.  This is what we wanted from ocfs2_xattr_value_buf.
Plus, moving the value buf up into ocfs2_xattr_set_entry() allows us to
pass it into ocfs2_xattr_set_value_outside() and ocfs2_xattr_cleanup().

Signed-off-by: Joel Becker <joel.becker@oracle.com>
Signed-off-by: Mark Fasheh <mfasheh@suse.com>