[kernel] fix mtd warnings

[kernel] fix mtd warnings

Fixes for the following warnings:

drivers/mtd/devices/block2mtd.c: In function '_open_bdev':
drivers/mtd/devices/block2mtd.c:272:3: warning: ISO C90 forbids mixed declarations and code
drivers/mtd/devices/block2mtd.c: In function 'add_device':
drivers/mtd/devices/block2mtd.c:399:13: warning: assignment discards qualifiers from pointer target type

In the case of 442-block2mtd_probe.patch, it's not until the insertion of a executable statement before the definition that causes a warning, so I've chosen to resolve the issue here by splitting the definition and the initialization into a definition and a statement (and assignment) instead.

Signed-off-by: Philip Prindeville <philipp@redfish-solutions.com>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@27007 3c298f89-4303-0410-b956-a3cf2f4a3e73