selftests/powerpc: Add tlbie_test in .gitignore

The commit identified below added tlbie_test but forgot to add it in
.gitignore.

Fixes: 93cad5f789 ("selftests/powerpc: Add test case for tlbie vs mtpidr ordering issue")
Cc: stable@vger.kernel.org # v5.4+
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/259f9c06ed4563c4fa4fa8ffa652347278d769e7.1582847784.git.christophe.leroy@c-s.fr

tools/testing/selftests/powerpc/mm/.gitignore

@@ -6,3 +6,4 @@ segv_errors
 wild_bctr
 large_vm_fork_separation
 bad_accesses
+tlbie_test