util: Canonicalize path to platform/ec
util: Canonicalize path to platform/ec

The script is getting different paths depending on which directory it
is called from.  Resolving the ec_dir should fix this.

BRANCH=None
BUG=b:236386294
TEST=(cd ~ ; ~/chromiumos/src/platform/ec/util/check_clang_format.py)
TEST=(cd ~/chromiumos/src/platform/ec; ~/chromiumos/src/platform/ec/util/check_clang_format.py)
TEST=(cd ~/chromiumos/src/platform/ec/zephyr; ~/chromiumos/src/platform/ec/util/check_clang_format.py)

Change-Id: I239db6ad77f636cfc7592e9879b1abc0933fa0c9
Signed-off-by: Jeremy Bettis <4df7b5147fee087dca33c181f288ee7dbf56e022@google.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3789832
Commit-Queue: Jeremy Bettis <4df7b5147fee087dca33c181f288ee7dbf56e022@chromium.org>
Reviewed-by: Tristan Honscheid <1e17951ff5ffc8afe254954c03de64afef62fe52@google.com>
Tested-by: Jeremy Bettis <4df7b5147fee087dca33c181f288ee7dbf56e022@chromium.org>

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