RFR: 8297874: get_dump_directory() in jfrEmergencyDump.cpp should pass correct length to jio_snprintf

[Calvin Cheung]

Please review this simple fix for correcting the length passing to` jio_snprintf `in the `get_dump_directory()` function in `jfrEmergencyDump.cpp`.

Passed tiers 1 - 4 testing.

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Commit messages:
 - 8297874: get_dump_directory() in jfrEmergencyDump.cpp should pass correct length to jio_snprintf

Changes: https://git.openjdk.org/jdk/pull/11916/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11916&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8297874
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/11916.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11916/head:pull/11916

PR: https://git.openjdk.org/jdk/pull/11916