USB: gadgetfs: remove unnecessary assignment

The dev_config() routine in gadgetfs has a check that
dev->dev->bNumConfigurations is equal to 1, and then contains a
redundant line of code setting the value to 1.  This patch removes the
unnecessary assignment.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>