libertas: Use new structure for SPI transfer delays

In a recent change to the SPI subsystem [1], 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).

[1] commit bebcfd27 ("spi: introduce `delay` field for
`spi_transfer` + spi_transfer_delay_exec()")
Signed-off-by: NSergiu Cuciurean <sergiu.cuciurean@analog.com>
Signed-off-by: NKalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/marvell/libertas/if_spi.c

@@ -235,8 +235,9 @@ static int spu_read(struct if_spi_card *card, u16 reg, u8 *buf, int len)
 		spi_message_add_tail(&dummy_trans, &m);
 	} else {
 		/* Busy-wait while the SPU fills the FIFO */
-		reg_trans.delay_usecs =
+		reg_trans.delay.value =
 			DIV_ROUND_UP((100 + (delay * 10)), 1000);
+		reg_trans.delay.unit = SPI_DELAY_UNIT_USECS;
 	}
 
 	/* read in data */