util/lint: use env to locate the bash binary

Otherwise there will, after make gitconfig,
be (hidden) shell command failures with 'git commit -s':
gmake: util/lint/check-style: Command not found
gmake: *** [Makefile.inc:632: check-style] Error 127

Change-Id: I3891dee53702ee10e5e44dae408193e49d7a89f1
Signed-off-by: Idwer Vollering <vidwer@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/38227
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

util/lint/check-style

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 # git pre-commit hook that runs an clang-format stylecheck.
 # Features:
 #  - abort commit when commit does not comply with the style guidelines