spi: spidev: Convert BUILD_BUG_ON() to static_assert()

static_assert() is a preferred method to fail build when the certain
constraints are not met. Convert BUILD_BUG_ON() to static_assert().

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20220323140215.2568-2-andriy.shevchenko@linux.intel.com


Signed-off-by: Mark Brown <broonie@kernel.org>