gen_compile_commands: lower the entry count threshold

[ Upstream commit cb36955a

 ]

Running gen_compile_commands.py after building the kernel with
allnoconfig gave this:

$ ./scripts/gen_compile_commands.py
WARNING: Found 449 entries. Have you compiled the kernel?

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>