scripts/faddr2line: Remove call to addr2line from find_dir_prefix()

Use the single long-running faddr2line process from find_dir_prefix().

Signed-off-by: Brian Johannesmeyer <bjohannesmeyer@gmail.com>
Link: https://lore.kernel.org/r/20240415145538.1938745-7-bjohannesmeyer@gmail.com


Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>