spi: pxa2xx: Move is_lpss_ssp() tests to caller

Move is_lpss_ssp() tests from functions to caller. Although this aims to
improve readability it also saves a few code bytes on x86.

Signed-off-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>