[SCSI] isci: remove IDEV_EH hack to disable "discovery-time" ata resets

Prior to commit 61aaff49

 "isci: filter broadcast change notifications
during SMP phy resets" we borrowed the MVS_DEV_EH approach from the
mvsas driver for preventing ->lldd_I_T_nexus_reset() events during ata
discovery.  This hack was protecting against the old ->phy_reset() in
ata_bus_probe(), but since the conversion to the new error handling this
hack is preventing resets from reaching ata devices.

Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>