perf bench: Fix perf bench syscall loop count

perf bench: Fix perf bench syscall loop count

Command 'perf bench syscall fork -l 100000' offers option -l to run for
a specified number of iterations. However this option is not always
observed. The number is silently limited to 10000 iterations as can be
seen:

Output before:
 # perf bench syscall fork -l 100000
 # Running 'syscall/fork' benchmark:
 # Executed 10,000 fork() calls
     Total time: 23.388 [sec]

    2338.809800 usecs/op
            427 ops/sec
 #

When explicitly specified with option -l or --loops, also observe
higher number of iterations:

Output after:
 # perf bench syscall fork -l 100000
 # Running 'syscall/fork' benchmark:
 # Executed 100,000 fork() calls
     Total time: 716.982 [sec]

    7169.829510 usecs/op
            139 ops/sec
 #

This patch fixes the issue for basic execve fork and getpgid.

Fixes: ece7f7c0507c ("perf bench syscall: Add fork syscall benchmark")
Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>
Acked-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
Tested-by: Athira Rajeev <atrajeev@linux.ibm.com>
Cc: Tiezhu Yang <yangtiezhu@loongson.cn>
Link: https://lore.kernel.org/r/20250304092349.2618082-1-tmricht@linux.ibm.com
Signed-off-by: Namhyung Kim <namhyung@kernel.org>