checkpatch: handle casts better fixing false categorisation of : as binary

The following incantation is triggering categorisation of its colon (:) as
a binary form, which it is not:

	return foo ? (s8)bar : baz;

Handle casts differently from types in the categoriser, allowing us to
better track (s8)bar as a value and not a declaration.

Reported-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>