spi: Remove unneeded OF node NULL checks

In the couple of places the NULL check of OF node is implied by the call
that takes it as a parameter. Drop the respective duplicate checks.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20230710154932.68377-2-andriy.shevchenko@linux.intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>