RFR: 8278336: Use int64_t to represent byte quantities consistently in JfrObjectAllocationSample

[Markus Grönlund]

Greetings,

please help review this small alignment to the types used in JfrObjectAllocationSample.

Testing: jdk_jfr

Thanks
Markus

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Commit messages:
 - 8272363

Changes: https://git.openjdk.java.net/jdk/pull/6736/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6736&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8278336
  Stats: 7 lines in 1 file changed: 0 ins; 0 del; 7 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6736.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6736/head:pull/6736

PR: https://git.openjdk.java.net/jdk/pull/6736