net: smc: fix missing brace warning for old compilers

For older versions of gcc, the array = {0}; will cause warnings:

net/smc/smc_llc.c: In function 'smc_llc_add_link_local':
net/smc/smc_llc.c:1212:9: warning: missing braces around initializer [-Wmissing-braces]
  struct smc_llc_msg_add_link add_llc = {0};
         ^
net/smc/smc_llc.c:1212:9: warning: (near initialization for 'add_llc.hd') [-Wmissing-braces]
net/smc/smc_llc.c: In function 'smc_llc_srv_delete_link_local':
net/smc/smc_llc.c:1245:9: warning: missing braces around initializer [-Wmissing-braces]
  struct smc_llc_msg_del_link del_llc = {0};
         ^
net/smc/smc_llc.c:1245:9: warning: (near initialization for 'del_llc.hd') [-Wmissing-braces]

2 warnings generated

Fixes: 4dadd151

 ("net/smc: enqueue local LLC messages")
Signed-off-by: Pujin Shi <shipujin.t@gmail.com>
Acked-by: Karsten Graul <kgraul@linux.ibm.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>