maple_tree: Clean up mas_parent_enum()

maple_tree: Clean up mas_parent_enum()

mas_parent_enum() is a simple wrapper for mte_parent_enum() which is
only called from that wrapper.  Remove the wrapper and inline
mte_parent_enum() into mas_parent_enum().

At the same time, clean up the bit masking of the root pointer since it
cannot be set by the time the bit masking occurs.  Change the check on
the root bit to a WARN_ON(), and fix the verification code to not
trigger the WARN_ON() before checking if the node is root.

Reported-by: Wei Yang <richard.weiyang@gmail.com>
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>