USB: xhci - fix bit definitions for IMAN register

According to XHCI specification (5.5.2.1) the IP is bit 0 and IE is bit 1
of IMAN register. Previously their definitions were reversed.

Even though there are no ill effects being observed from the swapped
definitions (because IMAN_IP is RW1C and in legacy PCI case we come in
with it already set to 1 so it was clearing itself even though we were
setting IMAN_IE instead of IMAN_IP), we should still correct the values.

This patch should be backported to kernels as old as 2.6.36, that
contain the commit 4e833c0b

 "xhci: don't
re-enable IE constantly".

Signed-off-by: Dmitry Torokhov <dtor@vmware.com>
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Cc: stable@vger.kernel.org