net: stmmac: remove unnecessary LPI disable when enabling LPI

Remove the unnecessary LPI disable when enabling LPI - as noted in
previous commits, there will never be two consecutive calls to
stmmac_mac_enable_tx_lpi() without an intervening
stmmac_mac_disable_tx_lpi.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://patch.msgid.link/E1tffdi-003ZIH-5h@rmk-PC.armlinux.org.uk


Signed-off-by: Jakub Kicinski <kuba@kernel.org>