spi: mchp-pci1xxxx: Fix length of SPI transactions not set properly in driver

spi: mchp-pci1xxxx: Fix length of SPI transactions not set properly in driver

In pci1xxxx_spi_transfer_one API, length of SPI transaction gets cleared
by setting of length mask. Set length of transaction only after masking
length field.

Fixes: 1cc0cbea7167 ("spi: microchip: pci1xxxx: Add driver for SPI controller of PCI1XXXX PCIe switch")
Signed-off-by: Tharun Kumar P <tharunkumar.pasumarthi@microchip.com>
Link: https://lore.kernel.org/r/20230404171613.1336093-2-tharunkumar.pasumarthi@microchip.com
Signed-off-by: Mark Brown <broonie@kernel.org>