bnxt_en: Fix strcpy() warnings in bnxt_ethtool.c

This patch fixes following smatch warnings:

drivers/net/ethernet/broadcom/bnxt/bnxt_ethtool.c:2826 bnxt_fill_coredump_seg_hdr() error: strcpy() '"sEgM"' too large for 'seg_hdr->signature' (5 vs 4)
drivers/net/ethernet/broadcom/bnxt/bnxt_ethtool.c:2858 bnxt_fill_coredump_record() error: strcpy() '"cOrE"' too large for 'record->signature' (5 vs 4)
drivers/net/ethernet/broadcom/bnxt/bnxt_ethtool.c:2879 bnxt_fill_coredump_record() error: strcpy() 'utsname()->sysname' too large for 'record->os_name' (65 vs 32)

Fixes: 6c5657d0 ("bnxt_en: Add support for ethtool get dump.")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Vasundhara Volam <vasundhara-v.volam@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>