ARM: tegra: clock: add i2c fast clock entry in clock table

Tegra's i2c controller require two clock sources named as
div-clk and fast-clk for proper operation.
Currently, the entry of fast-clk is missing in tegra30
clock table and it is incorrectly named in the tegra20
clock table.
Adds aliases to enable lookups for "fast-clk" to succeed.
A later patch will remove the incorrectly named clock,
once the driver is modified to use the new name.

Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Signed-off-by: Stephen Warren <swarren@nvidia.com>