Input: pmic8xxx-pwrkey - set sane default for debounce time

If the debounce time is 0 our usage of ilog2() later on in this driver will
cause undefined behavior. If CONFIG_OF=n this fact is evident to the
compiler, and it emits a call to ____ilog2_NaN() which doesn't exist. Fix
this by setting a sane default for debounce and failing to probe if
debounce is 0 in the DT.

Reported-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>