lib/crypto/poly1305: Fix arm64's poly1305_blocks_arch()

For some reason arm64's Poly1305 code got changed to ignore the padbit
argument.  As a result, the output is incorrect when the message length
is not a multiple of 16 (which is not reached with the standard
ChaCha20Poly1305, but bcachefs could reach this).  Fix this.

Fixes: a59e546 ("crypto: arm64/poly1305 - Add block-only interface")
Reported-by: Kent Overstreet <kent.overstreet@linux.dev>
Tested-by: Kent Overstreet <kent.overstreet@linux.dev>
Link: https://lore.kernel.org/r/20250616010654.367302-1-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>

Author: ebiggers

arch/arm64/lib/crypto/poly1305-glue.c

@@ -38,14 +38,14 @@ void poly1305_blocks_arch(struct poly1305_block_state *state, const u8 *src,
 			unsigned int todo = min_t(unsigned int, len, SZ_4K);
 
 			kernel_neon_begin();
-			poly1305_blocks_neon(state, src, todo, 1);
+			poly1305_blocks_neon(state, src, todo, padbit);
 			kernel_neon_end();
 
 			len -= todo;
 			src += todo;
 		} while (len);
 	} else
-		poly1305_blocks(state, src, len, 1);
+		poly1305_blocks(state, src, len, padbit);
 }
 EXPORT_SYMBOL_GPL(poly1305_blocks_arch);