Always use the correct pixel store size

Bug #7357394

When a bitmap is reused it may change configuration which can lead
to a different pixel store alignment. Our current texture cache
implementation assumes this never happens and keeps the old alignment
which can lead to distorted texture (if the bitmap goes from
ARGB8888 to RGB565 for instance.)

Change-Id: Ic57acf2403411ae4d0924e92f221298350612617