mtd_blkdevs.c: quiet a "symbol shadows" sparse warning

In register_mtd_blktrans(), the symbol 'ret' is already declared
as an int at the start of the function.  The inner loop declaration
is unnecessary.  Quiets the following sparse warning:

  warning: symbol 'ret' shadows an earlier one

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>