remove non-existent manpage reference
This function doesn't exist
@@ -131,7 +131,6 @@ On success
returns 0. On failure it returns
.BR -errno .
.SH SEE ALSO
-.BR io_uring_buf_ring_alloc (3),
.BR io_uring_buf_ring_add (3),
.BR io_uring_buf_ring_advance (3),
.BR io_uring_buf_ring_cq_advance (3)
