USB: docs: fixed table margin in configfs-usb-gadget-mass-storage

After merging forced_eject patch, there was a broken margin
in the configfs parameters table in the ABI documentation.
This patch fixes it.

Fixes: 421c8d9a20 ("usb: gadget: f_mass_storage: forced_eject attribute")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Maxim Devaev <mdevaev@gmail.com>
Link: https://lore.kernel.org/r/20220723101432.72178-1-mdevaev@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/ABI/testing/configfs-usb-gadget-mass-storage

@@ -19,7 +19,7 @@ KernelVersion:	3.13
 Description:
 		The attributes:
 
-		===========	==============================================
+		============	==============================================
 		file		The path to the backing file for the LUN.
 				Required if LUN is not marked as removable.
 		ro		Flag specifying access to the LUN shall be
@@ -38,4 +38,4 @@ Description:
 				regardless of whether the host has allowed it.
 				Any non-zero number of bytes written will
 				result in ejection.
-		===========	==============================================
+		============	==============================================