qemu-helper-native: Correctly pass program name as argv[0]

The previous version of this wasn't correctly passing the program name
as argv[0], and was also over-complicated anyway because argv[] is
guaranteed to be terminated with a NULL pointer, so it can be passed
directly to the execv'd process without needing to be copied.

Signed-off-by: Joshua Watt <JPEWhacker@gmail.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>