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: 421c8d9a20da ("usb: gadget: f_mass_storage: forced_eject attribute")
Reported-by: Stephen Rothwell <[e-mail]>
Signed-off-by: Maxim Devaev <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

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

···
 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
···
 				regardless of whether the host has allowed it.
 				Any non-zero number of bytes written will
 				result in ejection.
-		===========	==============================================
+		============	==============================================