bluetooth: hci_bcsp.c small cleanups/api users

Use bitrev16 from lib/bitrev.c.

Use the get_unaligned_be16 to get the crc from the packet, create a
small helper function for this.

Fix a shadowed variable sparse warning:
drivers/bluetooth/hci_bcsp.c:218:26: warning: symbol 'hdr' shadows an earlier one
drivers/bluetooth/hci_bcsp.c:187:5: originally declared here

[akpm@linux-foundation.org: select CONFIG_BITREVERSE, noted by akinobu.mita@gmail.com]
Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>