- switch to using BIT() macros
- use u8 instead of unsigned char for byte data
- use input_set_capability() instead of manipulating capabilities bits
  directly
- use sign_extend32() when extracting wheel data.
- do not abuse -1 as error code, propagate errors from various calls.
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>