test-media-patchstyle: Support utf-8 subjects

If we grep the patch file it will contain some weird email encoding
when processing utf-8 strings. Eg:

Subject: [PATCH v2 1/1] =?utf-8?q?media=3A_v4l2-core=3A_Replace_the_check_fo?=
        =?utf-8?q?r_firmware_registered_I=C2=B2C_devices?=

Let git log do the hard work for us.

Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>

test-media-patchstyle.sh

@@ -200,23 +200,26 @@ check_checkpatch() {
 }
 
 check_subject() {
+  sha=$1
   patch=$1
 
-  if grep -E -q "^Subject:.* Revert" "$patch"; then
+  subject=$(git log -n 1 --format=%s "$sha")
+
+  if echo "$subject" | grep -E -q "^Revert"; then
     return 0
   fi
 
   if python3 "$CI_DIR/lib/is-misc-only-patch.py"; then
     return 0
   elif python3 "$CI_DIR/lib/is-doc-only-patch.py"; then
-    if ! grep -E -q "^Subject:.* (doc|docs|Documentation|media):" "$patch"; then
+    if ! echo "$subject" | grep -E -q "^(doc|docs|Documentation|media):"; then
       echo "ERROR: $patch: Missing 'media:' or 'doc:' prefix in Subject" >&2 && return 1
     fi
   elif python3 "$CI_DIR/lib/is-dt-bindings-only-patch.py"; then
-    if ! grep -E -q "^Subject:.* (dt-bindings|media):" "$patch"; then
+    if ! echo "$subject" | grep -E -q "^(dt-bindings|media):"; then
       echo "ERROR: $patch: Missing 'media:' or 'dt-bindigs:' prefix in Subject" >&2 && return 1
     fi
-  elif ! grep -q "^Subject:.* media:" "$patch"; then
+  elif ! echo "$subject" | grep -q "^media:"; then
     echo "ERROR: $patch: Missing 'media:' prefix in Subject" >&2 && return 1
   fi
   return 0
@@ -250,7 +253,7 @@ if ! check_checkpatch "$PATCH"; then
   errno=1
 fi
 
-if ! check_subject "$PATCH"; then
+if ! check_subject "$sha" "$PATCH"; then
   errno=1
 fi