linux-user/syscall.c: clean up local variable shadowing in TARGET_NR_getcpu

linux-user/syscall.c: clean up local variable shadowing in TARGET_NR_getcpu

Fix following warnings:

.../linux-user/syscall.c: In function 'do_syscall1':
.../linux-user/syscall.c:11180:22: warning: declaration of 'cpu' shadows a previous local [-Wshadow=local]
11180 |             unsigned cpu, node;
      |                      ^~~
.../linux-user/syscall.c:8963:15: note: shadowed declaration is here
 8963 |     CPUState *cpu = env_cpu(cpu_env);
      |               ^~~

Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Message-ID: <20230925151029.461358-5-laurent@vivier.eu>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>