staging: most: usb: init return value in default path of switch/case expression

This patch avoids returning an uninitialized value in the default
path of the switch expression.

Signed-off-by: Christian Gromm <[e-mail]>
Reported-by: Dan Carpenter <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/staging/most/usb/usb.c

···
 		break;
 	default:
 		dev_warn(dev, "Query frame size of non-streaming channel\n");
+		frame_size = 0;
 		break;
 	}
 	return frame_size;