ofnet: Fix build regression in grub_ieee1275_parse_bootpath()

ofnet: Fix build regression in grub_ieee1275_parse_bootpath()

The grub_ieee1275_parse_bootpath() function (commit a661a32, ofnet: Initialize
structs in bootpath parser) introduces a build regression on SPARC:

cc1: warnings being treated as errors
net/drivers/ieee1275/ofnet.c: In function 'grub_ieee1275_parse_bootpath':
net/drivers/ieee1275/ofnet.c:156: error: missing initializer
net/drivers/ieee1275/ofnet.c:156: error: (near initialization for 'client_addr.type')
net/drivers/ieee1275/ofnet.c:156: error: missing initializer
net/drivers/ieee1275/ofnet.c:156: error: (near initialization for 'gateway_addr.type')
net/drivers/ieee1275/ofnet.c:156: error: missing initializer
net/drivers/ieee1275/ofnet.c:156: error: (near initialization for 'subnet_mask.type')
net/drivers/ieee1275/ofnet.c:157: error: missing initializer
net/drivers/ieee1275/ofnet.c:157: error: (near initialization for 'hw_addr.type')
make[3]: *** [net/drivers/ieee1275/ofnet_module-ofnet.o] Error 1

Initialize the entire structure.

More info can be found here:
  http://lists.gnu.org/archive/html/grub-devel/2018-03/msg00034.html

Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>