kernel_utils.cpp: Fix glibc-2.11 compilation issue.

With more recent GLibc, ::strstr() returns a const char*, not a char*

Change-Id: Id329ff6b7c0c876bd73bc2b18c1cc7267e666986
diff --git a/android/kernel/kernel_utils.cpp b/android/kernel/kernel_utils.cpp
index e396f4a..50b7094 100644
--- a/android/kernel/kernel_utils.cpp
+++ b/android/kernel/kernel_utils.cpp
@@ -125,12 +125,12 @@
                              &description)) {
         return false;
     }
-    char* bzImage = ::strstr(description.c_str(), "bzImage");
+    const char* bzImage = ::strstr(description.c_str(), "bzImage");
     if (!bzImage) {
         KERNEL_ERROR << "Not a compressed Linux kernel image!";
         return false;
     }
-    char* version = ::strstr(bzImage, "version ");
+    const char* version = ::strstr(bzImage, "version ");
     if (!version) {
         KERNEL_ERROR << "Could not determine version!";
         return false;