Add TOCK_EBADRVAL bad return variant error
Add TOCK_EBADRVAL bad return variant error

Add a BADRVAL error definition with an assigned value of 1024 as per
the Tock 2.0 system call TRD. This can be returned in case a driver
provides an unexpected system call return variant, which the userspace
wrapper does not know how to handle.

tock/libtock-c,tock/libtock-c,tock/libtock-c