prox_l2norm: use mu instead of 1/mu
prox_l2norm: use mu instead of 1/mu

frankong/bart,sidward/bart,Takishima/bart,Takishima/bart,sidward/bart,sdimoudi/bart,mrirecon/bart,sdimoudi/bart,mjacob75/bart,mrirecon/bart,mjacob75/bart,Takishima/bart,sdimoudi/bart,sdimoudi/bart,frankong/bart,sdimoudi/bart,frankong/bart,mrirecon/bart,mjacob75/bart,frankong/bart,mrirecon/bart,mjacob75/bart,frankong/bart,sidward/bart,Takishima/bart,mjacob75/bart,sidward/bart,mrirecon/bart,sidward/bart,Takishima/bart