net: bnx2x: fix sparse warnings

this patch fixes following sparse warnings:

bnx2x_main.c:9172:6: warning: symbol 'bnx2x_stop_ptp' was not declared. Should it be static?
bnx2x_main.c:13321:6: warning: symbol 'bnx2x_register_phc' was not declared. Should it be static?
bnx2x_main.c:14638:5: warning: symbol 'bnx2x_enable_ptp_packets' was not declared. Should it be static?

Signed-off-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>