sh_eth: fix branch prediction in sh_eth_interrupt()

IIUC, likely()/unlikely() should apply to the whole *if* statement's
expression, not a part of it  -- fix such expression in  sh_eth_interrupt()
accordingly...

Fixes: 283e38db ("sh_eth: Fix serialisation of interrupt disable with interrupt & NAPI handlers")
Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: David S. Miller <davem@davemloft.net>