net: stmmac: fix stmmac_xdp_open() clk_ptp_ref error cleanup

net: stmmac: fix stmmac_xdp_open() clk_ptp_ref error cleanup

Neither stmmac_xdp_release() nor the normal paths of stmmac_xdp_open()
touch clk_ptp_ref, so stmmac_xdp_open() should not be doing anything
with this clock. However, in its error path, it calls
stmmac_hw_teardown() which disables and unprepares this clock, which
can lead to the clock state becoming unbalanced when the netdev is
taken administratively down.

Remove this call to stmmac_hw_teardown(), and as this is the last user
of this function, remove the function as well.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>