minigbm: format_modifiers[0] -> format_modifier

The early version of the modifier assumed per plane modifiers.
The current version is only one modifier per buffer object.

BUG=none
TEST=compile

Change-Id: Ic3899118d44cb172ee2e4eae346e98cdf8328cf9
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/minigbm/+/2654590
Tested-by: Gurchetan Singh <[email protected]>
Reviewed-by: Gurchetan Singh <[email protected]>
Commit-Queue: Gurchetan Singh <[email protected]>
11 files changed