misc: mic: host driver sysfs cleanups.

+ Use DEVICE_ATTR_RO/RW instead of DEVICE_ATTR
+ Use ATTRIBUTE_GROUPS

These changes were suggested by Greg Kroah-Hartman during the
code review @ https://lkml.org/lkml/2013/9/6/13

Reported-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Signed-off-by: Dasaratharaman Chandramouli <dasaratharaman.chandramouli@intel.com>
Signed-off-by: Nikhil Rao <nikhil.rao@intel.com>
Signed-off-by: Harshavardhan R Kharche <harshavardhan.r.kharche@intel.com>
Signed-off-by: Sudeep Dutt <sudeep.dutt@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>