net: stmmac: remove redundant enable of PMT irq

For dwmac4, GMAC_INT_DEFAULT_ENABLE already includes
GMAC_INT_PMT_EN, so it is redundant to check if hw->pmt
is set, and if so, setting the bit again.

For dwmac1000, GMAC_INT_DEFAULT_MASK does not include
GMAC_INT_DISABLE_PMT, so it is redundant to check if
hw->pmt is set, and if so, clearing an already cleared bit.

Improve code readability by removing this redundant code.

Signed-off-by: Niklas Cassel <niklas.cassel@axis.com>
Signed-off-by: David S. Miller <davem@davemloft.net>