mfd: Fix build breakage in omap-usb-host.c

'ARM: OMAP3: USB: Fix the EHCI ULPI PHY reset issue' removes the include for
linux/gpio.h from omap-usb-host.c. This include indirectly includes plat/cpu.h
which is required by omap-usb-host.c. Fix the build breakage by including
it directly.

Acked-by: Keshava Munegowda <keshava_mgowda@ti.com>
Acked-by: Kevin Hilman <khilman@ti.com>
Signed-off-by: Russ Dill <Russ.Dill@ti.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

drivers/mfd/omap-usb-host.c

@@ -25,6 +25,7 @@
 #include <linux/clk.h>
 #include <linux/dma-mapping.h>
 #include <linux/spinlock.h>
+#include <plat/cpu.h>
 #include <plat/usb.h>
 #include <linux/pm_runtime.h>