Fix training Conditional Random Fields on GPU (#5313)

[alle-pawols]

Fixes #5313 .

Changes proposed in this pull request:

• Added casting tensor to the proper device

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[epwalsh]

Thanks @alle-pawols, this looks good! Can you just add an entry to the CHANGELOG under the "Fixed" section?

[alle-pawols]

@epwalsh I've updated the CHANGELOG file.

[epwalsh]

Thanks @alle-pawols!