opencl: move lookup-gap check for kernel zuikkis to after it is set from opt_lg.

Introduced by https://github.com/veox/sgminer/commit/89d641628b79f03b0520f0eb2586275a23420a0f

Closes https://github.com/veox/sgminer/issues/172
opencl: move lookup-gap check for kernel zuikkis to after it is set from opt_lg.

Introduced by https://github.com/veox/sgminer/commit/89d641628b79f03b0520f0eb2586275a23420a0f

Closes https://github.com/veox/sgminer/issues/172