ethernet/arc/arc_emac - fix NAPI "work > weight" warning

Initially I improperly set a boundary for maximum number of input
packets to process on NAPI poll ("work") so it might be more than
expected amount ("weight").

This was really harmless but seeing WARN_ON_ONCE on every device boot is
not nice. So trivial fix ("<" instead of "<=") is here.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>

Cc: Vineet Gupta <vgupta@synopsys.com>
Cc: Mischa Jonker <mjonker@synopsys.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Grant Likely <grant.likely@linaro.org>
Cc: Rob Herring <rob.herring@calxeda.com>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: David S. Miller <davem@davemloft.net>