[scripts] Print full clang prebuilt dir from get_clang_version.py

e.g. clang-r416183b1 instead of just r416183b1.

Test: manually run the script
Change-Id: I993202ea97433f841e3127ecef46dec66fb9a8c9
diff --git a/scripts/get_clang_version.py b/scripts/get_clang_version.py
index 622fca1..f6efc5f 100755
--- a/scripts/get_clang_version.py
+++ b/scripts/get_clang_version.py
@@ -30,7 +30,7 @@
   with open(global_go) as infile:
     contents = infile.read()
 
-  regex_rev = r'\tClangDefaultVersion\s+= "clang-(?P<rev>r\d+[a-z]?\d?)"'
+  regex_rev = r'\tClangDefaultVersion\s+= "(?P<rev>clang-r\d+[a-z]?\d?)"'
   match_rev = re.search(regex_rev, contents)
   if match_rev is None:
     raise RuntimeError('Parsing clang info failed')