bpf, docs: Fixup cpumap sphinx >= 3.1 warning

Fixup bpf_map_update_elem() declaration to use a single line.

Reported-by: Akira Yokosawa <akiyks@gmail.com>
Signed-off-by: Maryam Tahhan <mtahhan@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Tested-by: Akira Yokosawa <akiyks@gmail.com>
Acked-by: Stanislav Fomichev <sdf@google.com>
Link: https://lore.kernel.org/bpf/20221113103327.3287482-1-mtahhan@redhat.com

Documentation/bpf/map_cpumap.rst

@@ -48,8 +48,7 @@ Userspace
     program will result in the program failing to load and a verifier warning.
 
 .. c:function::
-    int bpf_map_update_elem(int fd, const void *key, const void *value,
-                   __u64 flags);
+    int bpf_map_update_elem(int fd, const void *key, const void *value, __u64 flags);
 
  CPU entries can be added or updated using the ``bpf_map_update_elem()``
  helper. This helper replaces existing elements atomically. The ``value`` parameter