Do not change environment if crc error in all available U-Boot environments

swupdate tries to write a variable to the actual U-Boot environment. If there is no such environment, a mostly empty default environment is written + the variable. This behaviour breaks the compiled in default environment setting in U-Boot and a reboot will most propably not work as expected.

Signed-off-by: Daniel Schnell <daniel.schnell.extern@ifm.com>