core/cortex-m/mpu.c does not compile
core/cortex-m/mpu.c does not compile

Fix for loop to be compatible with the tools used in the builders

BUG=chromium:1175163, chromium:1175181
BRANCH=none
TEST=make buildall

Signed-off-by: Denis Brockus <6b21e8190fb5e373363fb95271367073a16474ef@google.com>
Change-Id: Ic4d6f1b8aea0e20391eeb0d9496275289a7e21fa
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2678794
Tested-by: Denis Brockus <6b21e8190fb5e373363fb95271367073a16474ef@chromium.org>
Auto-Submit: Denis Brockus <6b21e8190fb5e373363fb95271367073a16474ef@chromium.org>
Reviewed-by: Diana Z <cb2016afc7183e5356c690dc63b4ba817470501a@chromium.org>
Reviewed-by: Jae Hoon Kim <c12e0fbc1cb5394470ed25a289c6d100e9c2e1d6@chromium.org>
Commit-Queue: Diana Z <cb2016afc7183e5356c690dc63b4ba817470501a@chromium.org>

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