ARM: tegra30: clocks: Fix pciex clock registration

ARM: tegra30: clocks: Fix pciex clock registration

Registering pciex as peripheral clock instead of fixed clock
as tegra_perih_reset_assert(deassert) api of this clock api
gives warning and ultimately does not succeed to assert(deassert)

Signed-off-by: Jay Agarwal <jagarwal@nvidia.com>
Acked-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Mike Turquette <mturquette@linaro.org>