checkpatch: limit sN/uN matches to actual bit sizes

Limit our type matcher to the s/u/le/be etc sizes that actually exist to
prevent miss categorising s2 as a type.  Fix up the spelling of the error
also.

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>