[PATCH] uml: fix compilation for __CHOOSE_MODE addition

I had added the __CHOOSE_MODE syntax to fix some warnings with newer GCC's
in the uml-fix-cond-expr-as-lvalues-warning patch.

Here is the update from the version I sent to make it work also when only
one mode (TT or SKAS) is enabled.

Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>