selftests/bpf: Correct map_fd to data_fd in tailcalls

Get and check data_fd. It should not check map_fd again.

Meanwhile, correct some 'return' to 'goto out'.

Thank the suggestion from Maciej in "bpf, x64: Fix tailcall infinite
loop"[0] discussions.

[0] https://lore.kernel.org/bpf/e496aef8-1f80-0f8e-dcdd-25a8c300319a@gmail.com/T/#m7d3b601066ba66400d436b7e7579b2df4a101033

Fixes: 79d49ba0 ("bpf, testing: Add various tail call test cases")
Fixes: 3b037911 ("selftests/bpf: Add tailcall_bpf2bpf tests")
Fixes: 5e0b0a4c

 ("selftests/bpf: Test tail call counting with bpf2bpf and data on stack")
Signed-off-by: Leon Hwang <hffilwlqm@gmail.com>
Reviewed-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Link: https://lore.kernel.org/r/20230906154256.95461-1-hffilwlqm@gmail.com
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>