mtd: fix warnings due to 64-bit partition support

mtd: fix warnings due to 64-bit partition support

commit 39ac34473f3c96e77cbe03a49141771ed1639486 ("cmd_mtdparts: use 64
bits for flash size, partition size & offset") introduced warnings
in a couple places due to printf formats or pointer casting.

This patch fixes the warnings pointed out here:
http://lists.denx.de/pipermail/u-boot/2013-October/164981.html

Signed-off-by: Scott Wood <[email protected]>
Cc: York Sun <[email protected]>
Cc: Stefan Roese <[email protected]>
Cc: Paul Burton <[email protected]>
Cc: Tom Rini <[email protected]>