selftests/bpf: verifier/prevent_map_lookup converted to inline assembly

Test verifier/prevent_map_lookup automatically converted to use inline assembly.

This was a part of a series [1] but could not be applied becuase
another patch from a series had to be witheld.

[1] https://lore.kernel.org/bpf/20230421174234.2391278-1-eddyz87@gmail.com/

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20230421204514.2450907-1-eddyz87@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>