spi: fsi: Handle 9 to 15 byte transfers lengths

spi: fsi: Handle 9 to 15 byte transfers lengths

The trailing <len> - 8 bytes of transfer data in this size range is no
longer ignored.

Fixes: c8a4cc557783 ("spi: Add FSI-attached SPI controller driver")
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
Signed-off-by: Eddie James <eajames@linux.ibm.com>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Joel Stanley <joel@jms.id.au>
Link: https://lore.kernel.org/r/20200909222857.28653-2-eajames@linux.ibm.com
Signed-off-by: Mark Brown <broonie@kernel.org>