aacraid: Created new mutex for ioctl path

aac_mutex was used to create protect the ioctl path for only the compat
path, it would be make more sense to place mutex in aac_do_ioctl, which
is the main ioctl function call that handles all ioctl commands.

Created new mutex ioctl_mutex in struct aac_dev to protect switch case
in aac_do_ioctl and removed aac_mutex from aac_cfg_ioctl and
aac_compat_do_ioctl

Signed-off-by: Raghava Aditya Renukunta <RaghavaAditya.Renukunta@pmcs.com>
Reviewed-by: Tomas Henzl <thenzl@redhat.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>