tpm_tis_spi: use new 'delay' 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: Alexandru Ardelean <alexandru.ardelean@analog.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>