kernel: mtdsplit_uimage: use separated buffer for reading data

We shouldn't read data directly into the header struct, as some devices
(e.g. Edimax) need more bytes due to some extra header.

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>


git-svn-id: svn://svn.openwrt.org/openwrt/trunk@44414 3c298f89-4303-0410-b956-a3cf2f4a3e73