Bluetooth: Use hci dev number as AMP controller ID

Previously an offset was added to the hci dev number to generate the
AMP controller ID, because it was possible for the PAL to register
as hci0, and 0 is invalid for an AMP controller ID. Since this commit
462bf76d it is not possible for
the PAL to register as hci0, so this offset is no longer necessary.

Change-Id: I4b01ddca5fad3aebeb4c138b5aee8819bb146f3d
Signed-off-by: Peter Krystad <pkrystad@codeaurora.org>