doc: usb: Fix typo in gadget_configfs documentation

Fix the directory name from 'configfs' to 'configs'.
Signed-off-by: Jaejoong Kim <climbbb.kim@gmail.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

Documentation/usb/gadget_configfs.txt

@@ -226,7 +226,7 @@ $ rm configs/<config name>.<number>/<function>
 where <config name>.<number> specify the configuration and <function> is
 a symlink to a function being removed from the configuration, e.g.:
 
-$ rm configfs/c.1/ncm.usb0
+$ rm configs/c.1/ncm.usb0
 
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