i2c: stub: fix build warning regression

Commit 6c42778780c40c ("i2c: stub: use pr_fmt") changed the DEBUG
handling and caused build warnings. Revert back to the original.

Fixes: 6c42778780c40c ("i2c: stub: use pr_fmt")
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
1 file changed