USB: serial: io_edgeport: cap received transmit credits

In the Linux kernel, the following vulnerability has been resolved: USB: serial: io_edgeport: cap received transmit credits The interrupt-status packet reports transmit credits returned by the device. edge_interrupt_callback() adds the 16-bit value to txCredits without checking maxTxCredits. edge_write() uses txCredits minus the software FIFO count as the amount of data that fits. Since the FIFO is allocated with maxTxCredits bytes, txCredits exceeding maxTxCredits can cause OOB write in ring buffer. Cap accumulated credits at maxTxCredits. Conforming devices should never hit the cap.