cmd: clk: update result of do_clk_setfreq

Update the result of do_clk_setfreq and always returns a CMD_RET_ value
(-EINVAL was a possible result).

This patch avoid the CLI output "exit not allowed from main input shell."

Fixes: 7ab418fb ("clk: add support for setting clk rate from cmdline")
Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Reviewed-by: Sean Anderson <seanga2@gmail.com>
Link: https://lore.kernel.org/r/20220131172131.3.Iec2029edb7fc0b29e13bcb86058ad2f614f62779@changeid