bssl-crypto: use `as_ffi_ptr`.

For the usual reason: see `as_ffi_ptr` in the source for details.

Change-Id: If210c8f21d7a32bc3a792cbd326326941ba82e11
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/88807
Auto-Submit: Adam Langley <agl@google.com>
Reviewed-by: Xiangfei Ding <xfding@google.com>
Commit-Queue: Xiangfei Ding <xfding@google.com>

rust/bssl-crypto/src/tls12_prf.rs

diff --git a/rust/bssl-crypto/src/tls12_prf.rs b/rust/bssl-crypto/src/tls12_prf.rs
index e39eaf8..9c8fa35 100644
--- a/rust/bssl-crypto/src/tls12_prf.rs
+++ b/rust/bssl-crypto/src/tls12_prf.rs
@@ -22,7 +22,7 @@
 
 use bssl_sys::CRYPTO_tls1_prf;
 
-use crate::{digest, sealed, FfiMutSlice, ForeignTypeRef};
+use crate::{digest, sealed, FfiMutSlice, FfiSlice, ForeignTypeRef};
 
 /// The special pseudo-random function used by TLS 1.2
 pub struct Tls12Prf<A>(PhantomData<fn() -> A>);
@@ -40,8 +40,8 @@
         seed2: Option<&[u8]>,
         output: &mut [u8],
     ) -> Result<(), ()> {
-        let (seed2, seed2_len) = if let Some(seed) = seed2 {
-            (seed.as_ptr(), seed.len())
+        let (seed2_ptr, seed2_len) = if let Some(seed2) = seed2 {
+            (seed2.as_ffi_ptr(), seed2.len())
         } else {
             (core::ptr::null(), 0)
         };
@@ -54,13 +54,13 @@
                 A::get_md(sealed::SealedType).as_ptr(),
                 output.as_mut_ffi_ptr(),
                 output.len(),
-                secret.as_ptr(),
+                secret.as_ffi_ptr(),
                 secret.len(),
-                label.as_ptr(),
+                label.as_ffi_ptr(),
                 label.len(),
-                seed1.as_ptr(),
+                seed1.as_ffi_ptr(),
                 seed1.len(),
-                seed2,
+                seed2_ptr,
                 seed2_len,
             )
         };