clk: oxnas: Rename to clk_oxnas_gate

Rename clock ops to clk_oxnas_gate in ops and structures.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Michael Turquette <mturquette@baylibre.com>
Link: lkml.kernel.org/r/20161005150752.22618-4-narmstrong@baylibre.com