spi: Drop duplicate IDR allocation code in spi_register_controller()

Refactor spi_register_controller() to drop duplicate IDR allocation.
Instead of if-else-if branching use two sequential if:s, which allows
to re-use the logic of IDR allocation in all cases.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20230710154932.68377-3-andriy.shevchenko@linux.intel.com


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