env: increment redund flag on read fail

If one of the reads fails when importing redundant environments (a
single read failure), the env_flags wouldn't get initialized in
env_import_redund(). If a user then calls saveenv, the new environment
will have the wrong flags value. So on the next load the new environment
will be ignored.

While debugging this, I also noticed that env/sf.c was not correctly
handling a single read failure, as it would not check the crc before
assigning it to gd->env_addr.

Having a special error path for when there is a single read failure
seems unnecessary and may lead to future bugs. Instead collapse the
'single read failure' error to be the same as a 'single crc failure'.
That way env_check_redund() either passes or fails, and if it passes we
are guaranteed to have checked the CRC.

Signed-off-by: Brandon Maier <brandon.maier@rockwellcollins.com>
CC: Joe Hershberger <joe.hershberger@ni.com>
CC: Wolfgang Denk <wd@denx.de>
CC: Heiko Schocher <hs@denx.de>
Reviewed-by: Tom Rini <trini@konsulko.com>