nvme: Call pci_disable_device on the error path.

Commit 5706aca74fe4 ("NVMe: Don't unmap controller registers on reset"),
which backported b00a726a

 to the 4.4.y kernel introduced a
regression in which it didn't call pci_disable_device in the error path
of nvme_pci_enable.

Reported-by: Jiri Slaby <jslaby@suse.cz>
Embarassed-developer: Gabriel Krisman Bertazi <krisman@linux.vnet.ibm.com>
Signed-off-by: Gabriel Krisman Bertazi <krisman@linux.vnet.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>