scripts/faddr2line: Use /usr/bin/env bash for portability

scripts/faddr2line: Use /usr/bin/env bash for portability

The shebang `#!/bin/bash` assumes a fixed path for the bash interpreter.
This path does not exist on some systems, such as NixOS, causing the
script to fail.

Replace `/bin/bash` with the more portable `#!/usr/bin/env bash`.

Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>