ab8500-bm: Trivially fix up some incorrect and out-of-date comments

Some of the comments in the ab8500 drivers reflect the behaviour
of the original device. As this driver now supports newer devices
then these comments are now redundant. Also some IRQ comments are
incorrect.

Signed-off-by: Marcus Cooper <marcus.xm.cooper@stericsson.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Reviewed-by: Rabin VINCENT <rabin.vincent@stericsson.com>
Tested-by: Rabin VINCENT <rabin.vincent@stericsson.com>