spi: spi-mem: zynq-qspi: Fix build error on architectures missing readsl/writesl

Alpha and some of the architectures are missing readsl/writesl functions.
so the zynq-qspi driver won't be able to build on these arches. hence use
ioread32_rep()/iowrite32_rep() instead of readsl()/writesl().

Signed-off-by: Naga Sureshkumar Relli <naga.sureshkumar.relli@xilinx.com>
Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>