coremark: fix error when it was built in the second run

coremark: fix error when it was built in the second run

When there is an error building packages other than coremark
and re-run with make -j1 V=s, the coremark package will report error.
the root cause is the folder was already created in the first run,
and not removed before the second run.

To fix this, use 'mkdir -p' instead of 'mkdir'.

Co-authored-by: Jonas Gorski <[email protected]>
Signed-off-by: Rye Sears <[email protected]>