tools: 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

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

tools/mtd-utils/patches/200-libubigen-add-ubigen_write_terminator-function.patch

@@ -77,7 +77,7 @@
  out_free:
 --- a/include/libubigen.h
 +++ b/include/libubigen.h
-@@ -188,6 +188,9 @@ int ubigen_write_layout_vol(const struct
+@@ -187,6 +187,9 @@ int ubigen_write_layout_vol(const struct
  			    long long ec1, long long ec2,
  			    struct ubi_vtbl_record *vtbl, int fd);