stmmac: fix sparse warnings

stmmac: fix sparse warnings

This patch fixes the following sparse warnings.

drivers/net/ethernet/stmicro/stmmac/enh_desc.c:381:30: warning: symbol 'enh_desc_ops' was not declared. Should it be static?
drivers/net/ethernet/stmicro/stmmac/norm_desc.c:253:30: warning: symbol 'ndesc_ops' was not declared. Should it be static?
drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c:141:33: warning: symbol 'stmmac_ptp' was not declared. Should it be static?

There is no functional change.

Signed-off-by: Andy Shevchenko <[email protected]>
Acked-by: Giuseppe CAVALLARO <[email protected]>
Signed-off-by: David S. Miller <[email protected]>