gralloc: Fix reserved region fd check

... as fd 0 is potentially valid.

BUG=b:207388558
TEST=cvd start
TEST=vts -m VtsHalGraphicsMapperV4_0Target

Change-Id: Idc31e294b2797491517f5d82e5ccd05a351a0cd4
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/minigbm/+/3441404
Reviewed-by: Yiwei Zhang <zzyiwei@chromium.org>
Reviewed-by: Roman Stratiienko <r.stratiienko@gmail.com>
Tested-by: Jason Macnak <natsu@google.com>
Commit-Queue: Jason Macnak <natsu@google.com>
1 file changed