net: hsr: fix incorrect type usage for protocol variable

Fix following sparse checker warning:-

net/hsr/hsr_slave.c:38:18: warning: incorrect type in assignment (different base types)
net/hsr/hsr_slave.c:38:18:    expected unsigned short [unsigned] [usertype] protocol
net/hsr/hsr_slave.c:38:18:    got restricted __be16 [usertype] h_proto
net/hsr/hsr_slave.c:39:25: warning: restricted __be16 degrades to integer
net/hsr/hsr_slave.c:39:57: warning: restricted __be16 degrades to integer

Signed-off-by: Murali Karicheri <m-karicheri2@ti.com>
Acked-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>