spi: spi-mem: Fix spi_mem_poll_status()

spi: spi-mem: Fix spi_mem_poll_status()

In spi_mem_exec_op(), in case cs_gpiod descriptor is set, exec_op()
callback can't be used.
The same must be applied in spi_mem_poll_status(), poll_status()
callback can't be used, we must use the legacy path using
read_poll_timeout().

Tested on STM32mp257c-ev1 specific evaluation board on which a
spi-nand was mounted instead of a spi-nor.

Signed-off-by: Patrice Chotard <patrice.chotard@foss.st.com>
Tested-by: Patrice Chotard <patrice.chotard@foss.st.com>
Link: https://lore.kernel.org/r/20220602091022.358127-1-patrice.chotard@foss.st.com
Signed-off-by: Mark Brown <broonie@kernel.org>