spi: zynq_spi: Fix infinite looping while xfer

During spi transfer, for example:
sspi 1:1.0 8 ff

the rx_len values will  be:
rx_len = 0
rx_len = 4294967295

This caused a busy looping during xfer, this patch fixes it
by adding a check while reading the rx fifo

Signed-off-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Cc: Michal Simek <michal.simek@xilinx.com>
Cc: Siva Durga Prasad Paladugu <sivadur@xilinx.com>
Reviewed-by: Jagan Teki <jteki@openedev.com>
1 file changed