Input: bfin_rotary - fix potential oops in interrupt handler

The interrupt handler in the driver tries to fetch driver data from
platform device, unfortunately it is only set up after interrupt handler
is registered. Since interrupt handler does not really need to access
the platform device itself let's change it to get the driver data
instance instead.

Acked-by: Sonic Zhang <sonic.zhang@analog.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>