drm/i915/gem: Do not look for the exact address in node

In preparation for the upcoming partial memory mapping feature,
we want to make sure that when looking for a node we consider
also the offset and not just the starting address of the virtual
memory node.

Signed-off-by: Andi Shyti <andi.shyti@linux.intel.com>
Reviewed-by: Nirmoy Das <nirmoy.das@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240807100521.478266-2-andi.shyti@linux.intel.com