gen_compile_commands: lower the entry count threshold

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>

scripts/gen_compile_commands.py

@@ -21,9 +21,9 @@ _LINE_PATTERN = r'^cmd_[^ ]*\.o := (.* )([^ ]*\.c)$'
 _VALID_LOG_LEVELS = ['DEBUG', 'INFO', 'WARNING', 'ERROR', 'CRITICAL']
 
 # A kernel build generally has over 2000 entries in its compile_commands.json
-# database. If this code finds 500 or fewer, then warn the user that they might
+# database. If this code finds 300 or fewer, then warn the user that they might
 # not have all the .cmd files, and they might need to compile the kernel.
-_LOW_COUNT_THRESHOLD = 500
+_LOW_COUNT_THRESHOLD = 300
 
 
 def parse_arguments():