drivers: spi: mchp_mss_qspi: Migrate spi_context_{complete,lock} usage

This commit updates the Microchip MSS QSPI SPI driver to reflect the
`spi_context_complete` and `spi_context_lock` function signature
changes introduced in the commit
4c204036.

Signed-off-by: Stephanos Ioannidis <root@stephanos.io>