perf trace: Fix wrong size to bpf_map__update_elem call

In linux-next
commit c7601744 ("perf cpumap: Reduce cpu size from int to int16_t")
causes the perf tests 100 126 to fail on s390:

Output before:
 # ./perf test 100
 100: perf trace BTF general tests         : FAILED!
 #

The root cause is the change from int to int16_t for the
cpu maps. The size of the CPU key value pair changes from
four bytes to two bytes. However a two byte key size is
not supported for bpf_map__update_elem().
Note: validate_map_op() in libbpf.c emits warning
 libbpf: map '__augmented_syscalls__': \
	 unexpected key size 2 provided, expected 4
when key size is set to int16_t.

Therefore change to variable size back to 4 bytes for
invocation of bpf_map__update_elem().

Output after:
 # ./perf test 100
 100: perf trace BTF general tests         : Ok
 #

Fixes: c7601744 ("perf cpumap: Reduce cpu size from int to int16_t")
Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>
Reviewed-by: Ian Rogers <irogers@google.com>
Acked-by: Howard Chu <howardchu95@gmail.com>
Cc: James Clark <james.clark@linaro.org>
Link: https://lore.kernel.org/r/20250324152756.3879571-1-tmricht@linux.ibm.com


Signed-off-by: Namhyung Kim <namhyung@kernel.org>