spi: xilinx_spi: Fix spi reset

It was incorrectly using an old priv->regs pointer, which was
initialized to zero. SPI resets won't happen on first call.

Signed-off-by: Jiajie Chen <c@jia.je>
Link: https://lore.kernel.org/r/20230227150938.211820-1-c@jia.je


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