amba drivers does not need to enable pm runtime at probe.
amba_probe already enables pm runtime.

This rids this warning in the ux500 boot log:
ssp-pl022 ssp0: Unbalanced pm_runtime_enable!
Signed-off-by: Michel JAOUEN <michel.jaouen@stericsson.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>