spi: pxa2xx: Extract clear_SSCR1_bits() helper

There are few places that repeat the logic of "clear some bits in SSCR1".
Extract clear_SSCR1_bits() helper to deduplicate that.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20210510124134.24638-12-andriy.shevchenko@linux.intel.com


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