motion_sense: Remove global fifo_flush_needed, redundant
motion_sense: Remove global fifo_flush_needed, redundant

Instead, use the event flag.

BUG=b:73557414
BRANCH=scarlet,poppy
TEST=Compile.

Change-Id: Ic1b123edb6f67012f38b1022d492492175b5d59d
Signed-off-by: Gwendal Grignou <190c5a5edfcf62e0246559bf31fa7548674de3ad@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1128551
Commit-Ready: ChromeOS CL Exonerator Bot <fa429e5907f00867f797423aea74327bb02c91b6@appspot.gserviceaccount.com>
Reviewed-by: Alexandru M Stan <1784cbba6d7675b1eba55eaefe41c7672ad9da3b@chromium.org>

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