usb: remove reference to deleted config STB03xxx

Commit 7583b63c ("powerpc/40x: Remove STB03xxx") removes the config
STB03xxx, but left a reference in ./drivers/usb/Kconfig behind.

Hence, ./scripts/checkkconfigsymbols.py warns:

STB03xxx
Referencing files: drivers/usb/Kconfig

Remove this reference to the deleted config.
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Link: https://lore.kernel.org/r/20210818071137.22711-4-lukas.bulwahn@gmail.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/Kconfig

@@ -11,7 +11,7 @@ config USB_OHCI_BIG_ENDIAN_MMIO
 
 config USB_OHCI_LITTLE_ENDIAN
 	bool
-	default n if STB03xxx || PPC_MPC52xx
+	default n if PPC_MPC52xx
 	default y
 
 config USB_EHCI_BIG_ENDIAN_MMIO