Provide an explicit match string for PXA3xx SSP ports.

Without this match string, SSP0/SSP1/SSP2 in PXA3xxx will be consided as
PXA27x SSP Port.
Signed-off-by: Daniel Mack <zonque@gmail.com>
Signed-off-by: Haojian Zhuang <haojian.zhuang@linaro.org>