debian: fix udeb package support

Previous commit which introduced SKIP_UDEB variable had typos in the
variable name in the m4 macros of control.in (UDEV vs. UDEB.) Fix those
typos and fix m4 quoting problem in "Don't".

Signed-off-by: Filipe Brandenburger <filbranden@google.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>