platform/x86: dell-wmi-sysman: Clean up security buffer helpers

platform/x86: dell-wmi-sysman: Clean up security buffer helpers

In calculate_security_buffer(), call strlen() once and use ALIGN() to
round up to an even size.

In populate_security_buffer(), also avoid recomputing strlen(), rename
the u32 pointer from 'seclen' to 'seclenp' to avoid confusion with the
new length variable, and drop the memcpy() guard since calling it with
size 0 is a no-op and therefore safe.

Use 'const char *' for the read-only source string in both helpers.

Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
Link: https://patch.msgid.link/20260331160310.608857-3-thorsten.blum@linux.dev
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>