clk: sunxi-ng: sun6i-a31: Fix register offset for mipi-csi clk

The register offset for the mipi-csi clk is off by 4, a copy paste
error from the mipi-dsi clk.

Fixes: c6e6c96d ("clk: sunxi-ng: Add A31/A31s clocks")
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>