usb: ehci-mv: Fix missing iomem in cast

usb: ehci-mv: Fix missing iomem in cast

Fix missing __iomem in cast to struct ehci_caps.  This fixes the Sparse
warning visible on x86_64 compile test:

   drivers/usb/host/ehci-mv.c:167:23: warning: cast removes address space '<asn:2>' of expression
   drivers/usb/host/ehci-mv.c:167:20: warning: incorrect type in assignment (different address spaces)
   drivers/usb/host/ehci-mv.c:167:20:    expected struct ehci_caps [noderef] <asn:2> *caps
   drivers/usb/host/ehci-mv.c:167:20:    got struct ehci_caps *

Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20200103164031.4089-1-krzk@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>