dtrace/arm64: properly traverse the symbol table

LINKER_EACH_FUNCTION_NAMEVAL() stops processing the symbol table if a
callback function returns a non-zero value.

The fbt_provide_module_function() callback should not return 1 when
ignoring symbols. Instead, always return 0, as in dtrace/x86.

Fixes: 30b68ecda84e ("Changes that improve DTrace FBT reliability on freebsd/arm64:")
Reviewed by: markj, oshogbo
Approved by: oshogbo (mentor)
Obtained from: CheriBSD
Differential Revision: https://reviews.freebsd.org/D53399