spi: tegra114: correct register name in definition

According to "Tegra K1 Processor Technical Reference Manual" (p. 2448),
bit 20 of SPI_COMMAND1 is called CS_SW_VAL and not CS_SS_VAL.

Signed-off-by: Ralf Ramsauer <ralf.ramsauer@oth-regensburg.de>
Signed-off-by: Mark Brown <broonie@kernel.org>