SCSI: remove unnecessary pci_set_drvdata()

Since commit 0998d063
(device-core: Ensure drvdata = NULL when no driver is bound),
the driver core clears the driver data to NULL after device_release
or on probe failure. Thus, it is not needed to manually clear the
device driver data to NULL.

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Cc: James Bottomley <JBottomley@parallels.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>