math_util: Fix rotation by identity.
math_util: Fix rotation by identity.

Rotation by identity matrix from a to b fails if a != b.

BUG=none
BRANCH=none
TEST=Use identity matrix in test motion_lid.c, check test passes.

Change-Id: I852132ee8cd67063921077cd0b7d848d10a730e0
Signed-off-by: Gwendal Grignou <190c5a5edfcf62e0246559bf31fa7548674de3ad@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/373722
Reviewed-by: Aseda Aboagye <12c9b286316a940fd31c24070da5ab64cdd4d0e7@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec