gralloc4-vts: update sampleIncrementInBits

sampleIncrementInBits is per sample not per component. An RGBA sample
is 32 bits not 8.

Test: VtsHalGraphicsMapperV4_0
Bug: 149310539

Change-Id: If4bd5aac87cada7040f52ee40159a72fa72a97be
1 file changed