Rename ptp to ptp_info.

Fix W=1 compile warnings (invalid kerneldoc):

drivers/net/ethernet/cavium/common/cavium_ptp.c:94: warning: Excess function parameter 'ptp' description in 'cavium_ptp_adjfine'
drivers/net/ethernet/cavium/common/cavium_ptp.c:141: warning: Excess function parameter 'ptp' description in 'cavium_ptp_adjtime'
drivers/net/ethernet/cavium/common/cavium_ptp.c:163: warning: Excess function parameter 'ptp' description in 'cavium_ptp_gettime'
drivers/net/ethernet/cavium/common/cavium_ptp.c:185: warning: Excess function parameter 'ptp' description in 'cavium_ptp_settime'
drivers/net/ethernet/cavium/common/cavium_ptp.c:208: warning: Excess function parameter 'ptp' description in 'cavium_ptp_enable'
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Wang Hai <wanghai38@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>