RFR: 8317335: Build on windows fails after 8316645

[Kim Barrett]

Please review this trivial change that fixes a build failure with Visual
Studio in Oracle's CI. The failure is a constant truncation warning because
the constant initial value of a `char` member is 0xaa, which is out of range
for a signed 8bit char. This change uses 0x7a as the initial value, which is
in the required range.

Note that the problem code successfully builds in GitHub Actions.  I don't
know why we're seeing this problem in Oracle's CI but not GA; perhaps a
difference in compiler versions?

Testing:
mach5 tier1

-------------

Commit messages:
 - change value of char initializer

Changes: https://git.openjdk.org/jdk/pull/16000/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16000&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8317335
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/16000.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16000/head:pull/16000

PR: https://git.openjdk.org/jdk/pull/16000