fix building when saveenv is disabled in some setups

fix building when saveenv is disabled in some setups

If you enable environment in the flash, but disable the embedded
option, and you disable the saveenv command, then the #if nested
logic will trigger a compile failure:
env_flash.c: In function 'env_relocate_spec':
env_flash.c:399: error: 'flash_addr' undeclared (first use in this function)
The fix is to add CMD_SAVEENV ifdef protection like everywhere else.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>