recovery-twrp: set RGBX_8888 color offsets only if not already initialized in inverse order

Workaround to achieve compatibility between the nameless oneplus
kernel and the framebuffer driver in omni's oppo kernel that still
expects color offsets in a non-standard inverse order (see change-id
I5068897f18e1d119a9bb7f1fe59f9b662153e1b0).

This fixes the failing framebuffer initializiation in twrp with the
nameless oneplus kernel.

Change-Id: I8a85809314596500ef8eb71797e098643299f22c