usb: ohci-pxa27x: include linux/dma-mapping.h

Include linux/dma-mapping.h to make the new functions available that are
used since 22d9d8e8

 ("DMA-API: usb: use dma_set_coherent_mask()").

drivers/usb/host/ohci-pxa27x.c: In function ‘ohci_pxa_of_init’:
drivers/usb/host/ohci-pxa27x.c:310:2: error: implicit declaration of function ‘dma_coerce_mask_and_coherent’ [-Werror=implicit-function-declaration]
drivers/usb/host/ohci-pxa27x.c:310:2: error: implicit declaration of function ‘DMA_BIT_MASK’ [-Werror=implicit-function-declaration]

Signed-off-by: Daniel Mack <zonque@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>