Hi,
the clock frequency is 40 MHz. This is also set in the dual config IP (see attached screenshot).
There is also a design contraint set for the clock
create_generated_clock -name ru_clk -divide_by 2 -master_clock PLL|altpll_component|auto_generated|pll1|clk[1] -source [get_pins -compatibility_mode { *altera_dual_boot:dual_boot_0|alt_dual_boot_avmm:alt_dual_boot_avmm_comp|alt_dual_boot:alt_dual_boot|ru_clk|clk }] [get_pins -compatibility_mode { *altera_dual_boot:dual_boot_0|alt_dual_boot_avmm:alt_dual_boot_avmm_comp|alt_dual_boot:alt_dual_boot|ru_clk|q } ]