ubifs: Fix assertion in layout_in_gaps()

An assertion in layout_in_gaps() verifies that the gap_lebs pointer is
below the maximum bound. When computing this maximum bound the idx_lebs
count is multiplied by sizeof(int), while C pointers arithmetic does take
into account the size of the pointed elements implicitly already. Remove
the multiplication to fix the assertion.

Fixes: 1e51764a ("UBIFS: add new flash file system")
Cc: <stable@vger.kernel.org>
Signed-off-by: Vincent Stehlé <vincent.stehle@intel.com>
Cc: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Richard Weinberger <richard@nod.at>