objtool: Rename --Werror to --werror

objtool: Rename --Werror to --werror

The objtool --Werror option name is stylistically inconsistent: halfway
between GCC's single-dash capitalized -Werror and objtool's double-dash
--lowercase convention, making it unnecessarily hard to remember.

Make the 'W' lower case (--werror) for consistency with objtool's other
options.

Acked-by: Petr Mladek <pmladek@suse.com>
Tested-by: Joe Lawrence <joe.lawrence@redhat.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>