scripts/gen_compile_commands.py: fix docstring

The referred tool is now in U-Boot. Replace "the Linux kernel" by
"U-Boot" to make the docstring coherent.

Signed-off-by: Joao Marcos Costa <jmcosta944@gmail.com>
Tested-by: Joao Paulo Goncalves <joao.goncalves@toradex.com>
diff --git a/scripts/gen_compile_commands.py b/scripts/gen_compile_commands.py
index 0227522..63d036a 100755
--- a/scripts/gen_compile_commands.py
+++ b/scripts/gen_compile_commands.py
@@ -5,7 +5,7 @@
 #
 # Author: Tom Roeder <tmroeder@google.com>
 #
-"""A tool for generating compile_commands.json in the Linux kernel."""
+"""A tool for generating compile_commands.json in U-Boot."""
 
 import argparse
 import json