rtla: Define __NR_sched_setattr for LoongArch

When executing "make -C tools/tracing/rtla" on LoongArch, there exists
the following error:

  src/utils.c:237:24: error: '__NR_sched_setattr' undeclared

Just define __NR_sched_setattr for LoongArch if not exist.

Link: https://lore.kernel.org/20250422074917.25771-1-yangtiezhu@loongson.cn
Reported-by: Haiyong Sun <sunhaiyong@loongson.cn>
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

Author: seehearfeel

tools/tracing/rtla/src/utils.c

@@ -227,6 +227,8 @@ long parse_ns_duration(char *val)
 #  define __NR_sched_setattr	355
 # elif __s390x__
 #  define __NR_sched_setattr	345
+# elif __loongarch__
+#  define __NR_sched_setattr	274
 # endif
 #endif