zynq: ps_spi: Generate proper node for the latest kernel driver

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
zynq: Fix qspi compatible string generation

Bug was introduced by this commit and was propagate
to the Linux kernel too.
"zynq: Use compact strings with zynq prefix"
(sha1: 3c696c24962e968553f9fc8dcb8dbdaaeea27359)

Signed-off-by: Michal Simek <michal.simek@xilinx.com>