bugfix in conv2d_c01b.Conv.lmul()

Symptom: MaxoutConvC01B was crashing on fprop() when the input space was set to a Conv2DSpace with axes other than ('c', 0, 1, 'b'). 

Cause: MaxoutConvC01B.fprop calls Conv.lmul, which is supposed to dimshuffle the axes from the input axes to ('c', 0, 1, 'b') before applying the convolution. Instead, due to a typo, it was dimshuffling from the input axes to the input axes, in effect doing nothing.

Fix: fixed the typo.