docs: kdoc: Expand 'at_least' when creating parameter list

docs: kdoc: Expand 'at_least' when creating parameter list

sphinx doesn't know that the kernel headers do:

    #define at_least static

Do this replacement before declarations are passed to it.

This prevents errors like the following from appearing once the
lib/crypto/ kernel-doc is wired up to the sphinx build:

   linux/Documentation/crypto/libcrypto:128: ./include/crypto/sha2.h:773: WARNING: Error in declarator or parameters
Error in declarator or parameters
Invalid C declaration: Expected ']' in end of array operator. [error at 59]
  void sha512_final (struct sha512_ctx *ctx, u8 out[at_least SHA512_DIGEST_SIZE])

Acked-by: Jonathan Corbet <corbet@lwn.net>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Tested-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://lore.kernel.org/r/20260418192138.15556-2-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>