tools/sched_ext: Add error logging for dsq creation failures in remaining schedulers

tools/sched_ext: Add error logging for dsq creation failures in remaining schedulers

Add scx_bpf_error() calls when scx_bpf_create_dsq() fails in the remaining
schedulers to improve debuggability:

- scx_simple.bpf.c: simple_init()
- scx_sdt.bpf.c: sdt_init()
- scx_cpu0.bpf.c: cpu0_init()
- scx_flatcg.bpf.c: fcg_init()

This follows the same pattern established in commit 2f8d489897ae
("sched_ext: Add error logging for dsq creation failures") for other
schedulers and ensures consistent error reporting across all schedulers.

Signed-off-by: zhidao su <suzhidao@xiaomi.com>
Signed-off-by: Tejun Heo <tj@kernel.org>