usb: musb: sunxi: Don't print error on MUSB_ULPI_BUSCONTROL access

Error message appears during suspend, where musb driver is storing
the register state in musb_save_context():
```
musb-sunxi 1c19000.usb: Error unknown readb offset 112
```

Print warning instead to avoid confusion.
Signed-off-by: Roman Stratiienko <r.stratiienko@gmail.com>
Link: https://lore.kernel.org/r/20211019131244.1568560-1-r.stratiienko@gmail.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/musb/sunxi.c

@@ -440,6 +440,10 @@ static u8 sunxi_musb_readb(void __iomem *addr, u32 offset)
 				return 0xde;
 
 			return readb(addr + SUNXI_MUSB_CONFIGDATA);
+		case MUSB_ULPI_BUSCONTROL:
+			dev_warn(sunxi_musb->controller->parent,
+				"sunxi-musb does not have ULPI bus control register\n");
+			return 0;
 		/* Offset for these is fixed by sunxi_musb_busctl_offset() */
 		case SUNXI_MUSB_TXFUNCADDR:
 		case SUNXI_MUSB_TXHUBADDR:
@@ -494,6 +498,10 @@ static void sunxi_musb_writeb(void __iomem *addr, unsigned offset, u8 data)
 			return writeb(data, addr + SUNXI_MUSB_TXFIFOSZ);
 		case MUSB_RXFIFOSZ:
 			return writeb(data, addr + SUNXI_MUSB_RXFIFOSZ);
+		case MUSB_ULPI_BUSCONTROL:
+			dev_warn(sunxi_musb->controller->parent,
+				"sunxi-musb does not have ULPI bus control register\n");
+			return;
 		/* Offset for these is fixed by sunxi_musb_busctl_offset() */
 		case SUNXI_MUSB_TXFUNCADDR:
 		case SUNXI_MUSB_TXHUBADDR: