ixgbe: Remove duplicate clear_bit() call

__IXGBE_RX_BUILD_SKB_ENABLED bit is already cleared.

Signed-off-by: Igor Pylypiv <igor.pylypiv@gmail.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>