libbpf: Fix whitespace in btf_add_composite() comment

Remove trailing space.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20210226202256.116518-3-iii@linux.ibm.com

tools/lib/bpf/btf.c

@@ -1883,7 +1883,7 @@ 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;