Remove explict use of ASCII encoding

Replace the use of CFStringGetCString with kCFStringEncodingASCII specified
with CFStringGetFileSystemRepresentation which will ensure the correct
character encoding is used to conver the CFString into a NULL terminated
char array suitable for use with POSIX APIs.

Change-Id: Ibab1dc05c4f4db8604d329a493b4241992b8e69d
diff --git a/fastboot/util_osx.c b/fastboot/util_osx.c
index a8f5c31..e718562 100644
--- a/fastboot/util_osx.c
+++ b/fastboot/util_osx.c
@@ -36,7 +36,7 @@
     CFStringRef executablePathString = CFURLCopyFileSystemPath(executableURL, kCFURLPOSIXPathStyle);
     CFRelease(executableURL);
 
-    CFStringGetCString(executablePathString, s, PATH_MAX-1, kCFStringEncodingASCII);
+    CFStringGetFileSystemRepresentation(executablePathString, s, PATH_MAX-1);
     CFRelease(executablePathString);
 
 	char *x;