spi: spi-zynq-qspi: Fix kernel-doc warning

Fix kernel-doc warning.

Signed-off-by: Amit Kumar Mahapatra <amit.kumar-mahapatra@xilinx.com>
Link: https://lore.kernel.org/r/20210429053802.17650-2-amit.kumar-mahapatra@xilinx.com


Signed-off-by: Mark Brown <broonie@kernel.org>