ovl: do not encode lower fh with upper sb_writers held

Merge Request Required Information

Summary of Changes

Fix to resolve a circular lock dependency was backported for the overlayfs. Regression testing: this kernel was booted up to login on a Ride SX 4.0 device

Signed-off-by: Aaron Brookner abrookne@redhat.com

Approved Development Ticket(s)

JIRA: https://issues.redhat.com/browse/RHEL-59837

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