perf bench: Fix NULL check against wrong variable

perf bench: Fix NULL check against wrong variable

We did a NULL check after "epollfdp = calloc(...)", but we checked
"epollfd" instead of "epollfdp".

Signed-off-by: Weiguo Li <[email protected]>
Acked-by: Davidlohr Bueso <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>