mtd-utils: Update to version 2.1.2

mtd-utils: Update to version 2.1.2

The release notes says this:
As already said, the changes since 2.1.1 are primarily bug fixes, addressing
compiler warnings and issues reported by diagnostic tools, but also build
failures for some configurations.
https://lists.infradead.org/pipermail/linux-mtd/2020-July/081299.html

The size of the ubi-utils ipk increases on mips BE by 0.2%
old:
ubi-utils_2.1.1-1_mips_24kc.ipk:	70992
new:
ubi-utils_2.1.2-1_mips_24kc.ipk:	71109

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>