driconf: initialize the option value before using it

ParseValue is freeing the pointer if the address is != 0. However,
since we allocate this value on the stack, we need to initialize the
data first.

Reviewed-by: Adam Jackson <ajax@redhat.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Signed-off-by: Martin Peres <martin.peres@mupuf.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7212>
1 file changed