Fix const-ness of strrchr callers.

This causes build failures in google3 where they use GCC. glibc only
provides const-correct overloads for string functions for GCC >= 4.4,
but clang -- which is what we use -- pretends to be GCC 4.2.

Change-Id: I2a054823ea6201ebcea46d5e77b80a975eefc622
diff --git a/adb/sysdeps.h b/adb/sysdeps.h
index 6160923..729bbcb 100644
--- a/adb/sysdeps.h
+++ b/adb/sysdeps.h
@@ -247,10 +247,10 @@
     return p;
 }
 
-static __inline__  char*  adb_dirstop( const char*  path )
+static __inline__  const char*  adb_dirstop( const char*  path )
 {
-    char*  p  = strrchr(path, '/');
-    char*  p2 = strrchr(path, '\\');
+    const char*  p  = strrchr(path, '/');
+    const char*  p2 = strrchr(path, '\\');
 
     if ( !p )
         p = p2;
@@ -521,12 +521,12 @@
 {
 }
 
-static __inline__ char*  adb_dirstart(const char*  path)
+static __inline__ const char*  adb_dirstart(const char*  path)
 {
     return strchr(path, '/');
 }
 
-static __inline__ char*  adb_dirstop(const char*  path)
+static __inline__ const char*  adb_dirstop(const char*  path)
 {
     return strrchr(path, '/');
 }