gpu-compute: Initialize GPUDriver member variables before use

A few member variables weren't initialized, but we were assuming that
they were 0 when first read. This explicitly sets those variables to 0.

Change-Id: I2c840d361ed3a7d306e22dc7561a3870f1ef94a1
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/46248
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Matt Sinclair <mattdsinclair@gmail.com>
Maintainer: Matt Sinclair <mattdsinclair@gmail.com>

src/gpu-compute/gpu_compute_driver.cc

@@ -53,7 +53,8 @@
 
 GPUComputeDriver::GPUComputeDriver(const Params &p)
     : EmulatedDriver(p), device(p.device), queueId(0),
-      isdGPU(p.isdGPU), gfxVersion(p.gfxVersion), dGPUPoolID(p.dGPUPoolID)
+      isdGPU(p.isdGPU), gfxVersion(p.gfxVersion), dGPUPoolID(p.dGPUPoolID),
+      eventPage(0), eventSlotIndex(0)
 {
     device->attachDriver(this);
     DPRINTF(GPUDriver, "Constructing KFD: device\n");