gralloc4: fix PlaneLayout encode typecasting

Fixes a bug where planeLayout members were being downcasted
to int32_t during the encoding step.

Bug: 168564125

Signed-off-by: SeYeong Byeon <sy.byeon@samsung.com>
Change-Id: I8d5139dbd253278193775380ca387d45bfe2589d
(cherry picked from commit 389ee533)