[BONDING]: fix sparse gfp nocast warnings

Fix implicit nocast warnings in bonding code:
drivers/net/bonding/bond_main.c:1302:49: warning: implicit cast to nocast type

Signed-off-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: David S. Miller <davem@davemloft.net>