selftests/bpf: Removed redundant fd after close in bpf_prog_load_log_buf

Removed unnecessary `fd = -1` assignments after closing file descriptors.
because it will be assigned by the function bpf_prog_load().This improves
code readability and removes redundant operations.

Signed-off-by: Zhu Jun <[e-mail]>
Signed-off-by: Andrii Nakryiko <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

tools/testing/selftests/bpf/prog_tests/log_buf.c

···
 	ASSERT_GE(fd, 0, "good_fd1");
 	if (fd >= 0)
 		close(fd);
-	fd = -1;
 
 	/* log_level == 2 should always fill log_buf, even for good prog */
 	log_buf[0] = '\0';
···
 	ASSERT_GE(fd, 0, "good_fd2");
 	if (fd >= 0)
 		close(fd);
-	fd = -1;
 
 	/* log_level == 0 should fill log_buf for bad prog */
 	log_buf[0] = '\0';
···
 	ASSERT_LT(fd, 0, "bad_fd");
 	if (fd >= 0)
 		close(fd);
-	fd = -1;
 
 	free(log_buf);
 }