spi: zynq_qspi: Read only one byte at a time from txbuf

spi: zynq_qspi: Read only one byte at a time from txbuf

Read only one byte at a time from txbuf as txbuf may not be
aligned and accessing more than a byte at a time may cause
alignment issues. This fixes the issue of data abort exception
while writing to flash device.

Signed-off-by: Siva Durga Prasad Paladugu <siva.durga.paladugu@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Ashok Reddy Soma <ashok.reddy.soma@xilinx.com>
Link: https://lore.kernel.org/r/20220131052240.23403-3-ashok.reddy.soma@xilinx.com