ide-generic: use ide_find_port() (take 3)

There should be no functional changes caused by this patch.

v2:
* Fix comment (noticed by Sergei Shtylyov).

v3:
* Fix no initalization of idx in some case. (Johann Felix Soden)

Cc: Johann Felix Soden <johfel@users.sourceforge.net>
Cc: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Cc: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>