staging: wilc1000: spi: Use new structure for SPI transfer delays

staging: wilc1000: spi: Use new structure for SPI transfer delays

In a recent change to the SPI subsystem in commit <bebcfd272df6>
("spi: introduce `delay` field for `spi_transfer` +
spi_transfer_delay_exec()"), a new `delay` struct was added
to replace the `delay_usecs`. This change replaces the current
`delay_usecs` with `delay` for this driver.

The `spi_transfer_delay_exec()` function [in the SPI framework] makes sure
that both `delay_usecs` & `delay` are used (in this order to preserve
backwards compatibility).

Signed-off-by: Sergiu Cuciurean <sergiu.cuciurean@analog.com>
Link: https://lore.kernel.org/r/20200304074319.22107-1-sergiu.cuciurean@analog.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>