stagefright_foundation: Fix parsing seek pre roll in Opus

Seek pre-roll parsing was skipped in OpusHeader because of
wrong loop check.

Also, C2 opus decoder plugin was reading from codecDelayBuf instead
of seekPreRollBuf

Test: With a local AMediaCodec api based application to decode
 opus encoder's output

Bug: 123426341
Change-Id: I0924f67c4a070a582b578d2ecdcd2fecd10134ad
diff --git a/media/codec2/components/opus/C2SoftOpusDec.cpp b/media/codec2/components/opus/C2SoftOpusDec.cpp
index 13e3df5..7dcd53d 100644
--- a/media/codec2/components/opus/C2SoftOpusDec.cpp
+++ b/media/codec2/components/opus/C2SoftOpusDec.cpp
@@ -318,7 +318,7 @@
             }
             if (seekPreRollBuf && seekPreRollBufSize == sizeof(uint64_t)) {
                 uint64_t value;
-                memcpy(&value, codecDelayBuf, sizeof(uint64_t));
+                memcpy(&value, seekPreRollBuf, sizeof(uint64_t));
                 mSeekPreRoll = ns_to_samples(value, kRate);
                 ++mInputBufferCount;
             }