PM / devfreq: tegra20: Silence deferred probe error

Tegra EMC driver was turned into a regular kernel driver, meaning that it
could be compiled as a loadable kernel module now. Hence EMC clock isn't
guaranteed to be available and clk_get("emc") may return -EPROBE_DEFER.
Let's silence the deferred probe error.

Acked-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>