block: Convert blk_invalidate_devt() header into a non-kernel-doc header

This patch avoids that the kernel-doc tool warns about this function
header when building with W=1.
Reviewed-by: Chaitanya Kulkarni <chiatanya.kulkarni@wdc.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/genhd.c

@@ -532,7 +532,7 @@ void blk_free_devt(dev_t devt)
 	}
 }
 
-/**
+/*
  * We invalidate devt by assigning NULL pointer for devt in idr.
  */
 void blk_invalidate_devt(dev_t devt)