usb: musb: Fix an error message

'ret' is known to be 0 here.
Initialize 'ret' with the expected error code before using it.

Fixes: 0990366b ("usb: musb: Add support for MediaTek musb controller")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/69f514dc7134e3c917cad208e73cc650cb9e2bd6.1620159879.git.christophe.jaillet@wanadoo.fr


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>