ieee1275/ofnet: Fix hw_addr variable initialization

The latest gcc does not like the initializer used for the
grub_net_link_level_address_t hw_addr variable:

../../grub-core/net/drivers/ieee1275/ofnet.c: In function ‘grub_ieee1275_parse_bootpath’:
../../grub-core/net/drivers/ieee1275/ofnet.c:158:3: warning: braces around scalar initializer
  158 |   grub_net_link_level_address_t hw_addr = {0, {{0, 0, 0, 0, 0, 0}}};
      |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../../grub-core/net/drivers/ieee1275/ofnet.c:158:3: note: (near initialization for ‘hw_addr.len’)
../../grub-core/net/drivers/ieee1275/ofnet.c:158:3: error: braces around scalar initializer
../../grub-core/net/drivers/ieee1275/ofnet.c:158:3: note: (near initialization for ‘hw_addr.len’)
../../grub-core/net/drivers/ieee1275/ofnet.c:158:52: warning: excess elements in scalar initializer
  158 |   grub_net_link_level_address_t hw_addr = {0, {{0, 0, 0, 0, 0, 0}}};
...

Since we're zeroing it anyways switch to a simpler initializer
to fix this.

Signed-off-by: Hans de Goede <johannes.goede@oss.qualcomm.com>

Author: Hans de Goede

grub-core/net/drivers/ieee1275/ofnet.c

@@ -155,7 +155,7 @@ grub_ieee1275_parse_bootpath (const char *devpath, char *bootpath,
   char *equal_char = 0;
   grub_size_t field_counter = 0;
   grub_net_network_level_address_t client_addr = {0, {0}, 0}, gateway_addr = {0, {0}, 0}, subnet_mask = {0, {0}, 0};
-  grub_net_link_level_address_t hw_addr = {0, {{0, 0, 0, 0, 0, 0}}};
+  grub_net_link_level_address_t hw_addr = {};
   grub_net_interface_flags_t flags = 0;
   struct grub_net_network_level_interface *inter = NULL;
   grub_uint16_t vlantag = 0;