kconfig/lxdialog: Use new mininimum resize definitions in conf_choice()

This is a cleanup which uses the proper (new) definitions and does
not change current behaviour.

Signed-off-by: Sedat Dilek <sedat.dilek@gmail.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Tested-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>

---
Yann had some more ideas on improvements:

"What would be nice is an improvement that scales the choice window to
the number of entries in the choice. If there are a lot of choice
entries, then the choice popup grows in height (but does not overflow
the screen of course). So, instead of seeing only 6 entries, we'd see
as much as possible in the current screen.

Ditto for the width: the popup adapts to the longest prompt (but does
not overflow the screen either, of course), so prompts are not
truncated."

NOTE: This patch requires [1].

[1] http://marc.info/?l=linux-kbuild&m=137128726917166&w=2