mei: revamp open handler counts

Make open counter to be incremented and decremented
from mei_cl_link and mei_cl_unlik function respectively

Nfc was assuming symmetric linking API and thus open handler
count was never decreased. This patch fixes that.
We need to add separate open hander count for amthif which
is handled out of link/unlink functions and doesn't break
the symmetric API.

Last we do not waste clients slots if amthif or wd are not present
in the device. we don't need to allocates slots ahead
it is all covered by link/unlink before the devices is responding
to user space connection and thus not racing on allocation

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/misc/mei/mei_dev.h

@@ -414,6 +414,7 @@ struct mei_device {
 	struct file *iamthif_file_object;
 	struct mei_cl iamthif_cl;
 	struct mei_cl_cb *iamthif_current_cb;
+	long iamthif_open_count;
 	int iamthif_mtu;
 	unsigned long iamthif_timer;
 	u32 iamthif_stall_timer;