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>
1 file changed