It was already increased for NAND devices so do the same for the ones
with serial memory.
Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Backport of r49207
git-svn-id: svn://svn.openwrt.org/openwrt/branches/chaos_calmer@49208 3c298f89-4303-0410-b956-a3cf2f4a3e73