Fix speed-profile compilation for prebuilds

We were testing the wrong variable when setting the dex2oat flags

Test: m; flash, dumpsys dexopt and check for speed-profile
Bug: 78515726

(cherry picked from commit 7d701355)

Merged-In: I57c0e11aab2e4879c3ba3b2851f356b5864f5da9
Change-Id: I2e2f9da1dc9ed71977ec1d698433674c731f78bc