libbpf: Fix whitespace in btf_add_composite() comment

mainline inclusion
from mainline-5.13-rc1
commit 1b1ce92b
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5EUVD
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=1b1ce92b24331b569a444858fc487a1ca19dc778

-------------------------------------------------

Remove trailing space.
Signed-off-by: NIlya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Acked-by: NYonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20210226202256.116518-3-iii@linux.ibm.com
(cherry picked from commit 1b1ce92b)
Signed-off-by: NWang Yufen <wangyufen@huawei.com>

tools/lib/bpf/btf.c

@@ -1889,7 +1889,7 @@ static int btf_add_composite(struct btf *btf, int kind, const char *name, __u32
  *   - *byte_sz* - size of the struct, in bytes;
  *
  * Struct initially has no fields in it. Fields can be added by
- * btf__add_field() right after btf__add_struct() succeeds. 
+ * btf__add_field() right after btf__add_struct() succeeds.
  *
  * Returns:
  *   - >0, type ID of newly added BTF type;