fix broken link for GenerationConfig

[xin3he]

Importing lm_eval stuffs will break the link between transformers.generation.GenerationConfig andtransformers.GenerationConfig.

You can reproduce it with code below.

from lm_eval import evaluator, utils
from optimum.habana.transformers.modeling_utils import adapt_transformers_to_gaudi
adapt_transformers_to_gaudi()
import transformers
print('=======', transformers.GenerationConfig)
print('=======', transformers.generation.GenerationConfig)

[HuggingFaceDocBuilderDev]

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