fix bug with gpu less than or equal to kernel
fix bug with gpu less than or equal to kernel

mrirecon/bart,grlee77/bart,sdimoudi/bart,sidward/bart,frankong/bart,mrirecon/bart,frankong/bart,Takishima/bart,nckz/bart,Takishima/bart,mjacob75/bart,mjacob75/bart,nckz/bart,Takishima/bart,sdimoudi/bart,sdimoudi/bart,sdimoudi/bart,mjacob75/bart,frankong/bart,mrirecon/bart,sidward/bart,grlee77/bart,sidward/bart,sidward/bart,grlee77/bart,grlee77/bart,nckz/bart,mrirecon/bart,sidward/bart,sdimoudi/bart,Takishima/bart,Takishima/bart,frankong/bart,mrirecon/bart,frankong/bart,mjacob75/bart,mjacob75/bart,nckz/bart,grlee77/bart,nckz/bart