Fix unwrap comment for CBB_init_fixed

Change-Id: I893930a8d23f49968883e4c9b8425ebcc5a2d23b
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/75007
Auto-Submit: David Benjamin <davidben@google.com>
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: David Benjamin <davidben@google.com>

rust/bssl-crypto/src/lib.rs

diff --git a/rust/bssl-crypto/src/lib.rs b/rust/bssl-crypto/src/lib.rs
index d1abb93..db03b55 100644
--- a/rust/bssl-crypto/src/lib.rs
+++ b/rust/bssl-crypto/src/lib.rs
@@ -476,8 +476,7 @@
             bssl_sys::CBB_init_fixed(cbb, boxed.as_mut_ptr() as *mut u8, len) == 1
         })
     }
-    // `CBB_init` only fails if out of memory, which isn't something that this
-    // crate handles.
+    // `CBB_init_fixed` never fails and does not allocate.
     .unwrap();
 
     func(&mut cbb);