clk: scmi: fix scmi_clk_get_attibute()

Local variable out.name lives on the stack and therefore cannot
be returned directly. Move the strdup() call into the function.
(Coverity 352460)

Fixes: 7c33f789 ("clk: scmi: register scmi clocks with CCF")
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Sean Anderson <seanga2@gmail.com>