include ehci-pci in auto_add_modules list

Linux v3.8 changes the name of the PCI ehci driver from ehci-hcd to
ehci-pci. Ref

| commit adfa79d1c06a32650332930ca4c488ca570b3407
| Author: Alan Stern <stern@rowland.harvard.edu>
| Date:   Thu Nov 1 11:13:04 2012 -0400
|
|     USB: EHCI: make ehci-pci a separate driver
|
|     This patch (as1625) splits the PCI portion of ehci-hcd out into its
|     own separate driver module, called ehci-pci.  Consistently with the
|     current practice, the decision whether to build this module is not
|     user-configurable.  If EHCI and PCI are enabled then the module will
|     be built, always.
|
|     Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
|     CC: Felipe Balbi <balbi@ti.com>
|     Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Thanks: Bjørn Mork <bjorn@mork.no> for bug report + patch
Closes: #700572