usb: dwc3: fix build warnings

fix the following build warnings:

drivers/usb/dwc3/core.c: In function ‘dwc3_uboot_init’:
drivers/usb/dwc3/core.c:625:6: warning: ‘dev’ is used uninitialized in this function [-Wuninitialized]
mem = devm_kzalloc(dev, sizeof(*dwc) + DWC3_ALIGN_MASK, GFP_KERNEL);
        ^
drivers/usb/dwc3/dwc3-omap.c: In function ‘dwc3_omap_uboot_init’:
drivers/usb/dwc3/dwc3-omap.c:380:7: warning: ‘dev’ is used uninitialized in this function [-Wuninitialized]
omap = devm_kzalloc(dev, sizeof(*omap), GFP_KERNEL);

Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/dwc3/core.c

@@ -613,7 +613,7 @@ static void dwc3_core_exit_mode(struct dwc3 *dwc)
 int dwc3_uboot_init(struct dwc3_device *dwc3_dev)
 {
 	struct dwc3		*dwc;
-	struct device		*dev;
+	struct device		*dev = NULL;
 	u8			lpm_nyet_threshold;
 	u8			tx_de_emphasis;
 	u8			hird_threshold;

drivers/usb/dwc3/dwc3-omap.c

@@ -374,7 +374,7 @@ static void dwc3_omap_set_utmi_mode(struct dwc3_omap *omap, int utmi_mode)
 int dwc3_omap_uboot_init(struct dwc3_omap_device *omap_dev)
 {
 	u32			reg;
-	struct device		*dev;
+	struct device		*dev = NULL;
 	struct dwc3_omap	*omap;
 
 	omap = devm_kzalloc(dev, sizeof(*omap), GFP_KERNEL);