usb: gadget: fsl_udc_core: fix compile error.

Fix compile error in file drivers/usb/gadget/fsl_udc_core.c.

drivers/usb/gadget/fsl_udc_core.c: In function 'portscx_device_speed':
drivers/usb/gadget/fsl_udc_core.c:1720: error: 'speed' undeclared (first
use in this function)

Introduced in commit e538dfda
(usb: Provide usb_speed_string() function)
Signed-off-by: Alexander Aring <a.aring@phytec.de>
Acked-by: Michal Nazarewicz <mina86@mina86.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/gadget/fsl_udc_core.c

@@ -1717,7 +1717,7 @@ static void dtd_complete_irq(struct fsl_udc *udc)
 
 static inline enum usb_device_speed portscx_device_speed(u32 reg)
 {
-	switch (speed & PORTSCX_PORT_SPEED_MASK) {
+	switch (reg & PORTSCX_PORT_SPEED_MASK) {
 	case PORTSCX_PORT_SPEED_HIGH:
 		return USB_SPEED_HIGH;
 	case PORTSCX_PORT_SPEED_FULL: