spi: microchip-core-qspi: don't attempt to transmit during emulated read-only dual/quad operations

In the Linux kernel, the following vulnerability has been resolved: spi: microchip-core-qspi: don't attempt to transmit during emulated read-only dual/quad operations The core will deal with reads by creating clock cycles itself, there's no need to generate clock cycles by transmitting garbage data at the driver level. Further, transmitting garbage data just bricks the transfer since QSPI doesn't have a dedicated master-out line like MOSI in regular SPI. I'm not entirely sure if the transfer is bricked because of the garbage data being transmitted on the bus or because the core loses track of whether it is supposed to be sending or receiving data.