xfsprogs: reset opterr on platform_getoptreset()

xfsprogs: reset opterr on platform_getoptreset()

Setting opterr = 0 is useful if you want to only parse a subset of
paremeters first. Later you will have to set opterr = 1 again, but
we already have a platform_getoptreset() and its expected to be used
in these contexts so just sprinkle it there.

Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>