selftests/bpf: remove reduplicated s32 casting in "crafted_cases"

The "S32_MIN" is already defined with s32 casting, so there is no need
to do it again.

Signed-off-by: Menglong Dong <menglong8.dong@gmail.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20231219134800.1550388-3-menglong8.dong@gmail.com


Signed-off-by: Alexei Starovoitov <ast@kernel.org>