USB: gadget: f_fs: fix memdup_user.cocci warnings

drivers/usb/gadget/function/f_fs.c:3829:8-15: WARNING opportunity for memdup_user

 Use memdup_user rather than duplicating its implementation
 This is a little bit restricted to reduce false positives

Generated by: scripts/coccinelle/api/memdup_user.cocci

Fixes: 8704fd73 ("USB: gadget: f_fs: remove likely/unlikely")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/r/20210308070951.GA83949@8a16bdd473dc


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>