greybus: gbuf: have caller set actual_length

A Greybus buffer has both a transfer_buffer_size field, which is the
size in bytes of the transfer buffer, and an actual_length field,
which is the number of bytes in that buffer that are actually
consumed.  The user of the buffer--and not the buffer allocation
method--should be setting the actual_length field.

Stop setting the actual length on the es1-ap-usb alloc_gbuf_data
method.  And *do* set it in gb_operation_create(), where we can
presume the operation being allocated will consume all the bytes
requested.
Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>

drivers/staging/greybus/es1-ap-usb.c

@@ -126,7 +126,6 @@ static int alloc_gbuf_data(struct gbuf *gbuf, unsigned int size, gfp_t gfp_mask)
 	buffer[0] = gbuf->cport_id;
 	gbuf->transfer_buffer = &buffer[1];
 	gbuf->transfer_buffer_length = size;
-	gbuf->actual_length = size;
 
 	/* When we send the gbuf, we need this pointer to be here */
 	gbuf->hdpriv = es1;

drivers/staging/greybus/operation.c

@@ -132,6 +132,7 @@ struct gb_operation *gb_operation_create(struct gb_connection *connection,
 		kfree(operation);
 		return NULL;
 	}
+	gbuf->actual_length = size;	/* Record what we'll use */
 
 	operation->connection = connection;		/* XXX refcount? */