Input: adxl34 - make enable/disable separate from suspend/resume

Suspending and resuming the device should be separate from enabling
and disabling it through sysfs attribute and thus should not alter
ac->disabled flag.

[michael.hennerich@analog.com: various fixups]
Tested-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>