stmmac: fix LPI TW timer value to 20.5us.

The value for LPI TW timer has to be updated to 0x1E that is the hardcoded value
of 20.5us and it will apply to all EEE enabled Remote PHYs.
Disadvantage is for PHY's that support lesser wakeup time but we can accept it
waiting to implement LLDP to negotiate the Wakeup time of Remote PHY.
Signed-off-by: Nnandini sharma <nandini.sharma@st.com>
Signed-off-by: NGiuseppe Cavallaro <peppe.cavallaro@st.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/stmicro/stmmac/common.h

@@ -287,7 +287,7 @@ struct dma_features {
 
 /* Default LPI timers */
 #define STMMAC_DEFAULT_LIT_LS	0x3E8
-#define STMMAC_DEFAULT_TWT_LS	0x0
+#define STMMAC_DEFAULT_TWT_LS	0x1E
 
 #define STMMAC_CHAIN_MODE	0x1
 #define STMMAC_RING_MODE	0x2