ide: Two fixes regarding memory allocation

In function ide_devset_execute() we should use __GFP_WAIT rather than
GFP_KERNEL. Also, the allocation cannot possibly fail at that point.
More importantly, there is a potential memory leak in the device probing
code. The infrastructure seems rather complex and I hope I haven't messed
anything up by trying to fix this.

Signed-off-by: Elias Oltmanns <eo@nebensachen.de>
[bart: remove superfluous ide_lock taking]
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>