cmd: clk: fix long help message

Fix the long help message for "clk setfreq" command

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/20220131172131.4.Ic863c28ffdcc15b3f4616434c2efd88b4e45495c@changeid