fw_printenv: Don't bail out directly after one env read error

When using a redundant environment a read error should simply mean to
not use that copy instead of giving up completely. The other copy may
be just fine.

Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>
Signed-off-by: Ioan-Adrian Ratiu <adrian.ratiu@ni.com>