lint: fix cppcheck warnings about redundant assignments/copies

This PR fixes or suppresses the `cppcheck` issued warnings about redundant assignments/copies.
For `sys/net` these occur because data is copied to a buffer that is set to 0 by memset before that. Since this makes sure that the buffer doesn't contain stale data I chose to suppress this warning.
For ` boards/redbee-econotag/tools/mc1322x-load.c` I've removed the first assignments because this will keep the behaviour as it was before.
For `cpu/arm_common/syscalls.c` I've chosen to supress the warnings as I'm not sure about the behaviour of `ff_*_r` which seem to be left over code from an old FAT module.
For `cpu/lpc2387/i2c/i2c.c` and the `drivers/*` I removed the initialization of the variables as the `i2c_*` command return a `bool` in any case.