fix runtime issues for scripts

now, some script to update kernel-headers is not working.
because of wrong variable value and test codes.
so this issue is fixed.

Change-Id: Iffae9607858cc3c1c58fa24244be217b5a1ab06e
diff --git a/libc/kernel/tools/generate_uapi_headers.sh b/libc/kernel/tools/generate_uapi_headers.sh
index 386159a..90ba0ed 100755
--- a/libc/kernel/tools/generate_uapi_headers.sh
+++ b/libc/kernel/tools/generate_uapi_headers.sh
@@ -159,7 +159,7 @@
   cd "${TMPDIR}"
   echo "Fetching android kernel source ${KERNEL_VERSION}"
   git clone https://android.googlesource.com/kernel/common.git
-  cd "${COMMON}"
+  cd "${src_dir}"
   git checkout "${KERNEL_VERSION}"
   KERNEL_DIR="${TMPDIR}"
 elif [[ "${KERNEL_DIR}" == "" ]]; then
@@ -180,6 +180,8 @@
   done
 fi
 
+cd ${ANDROID_BUILD_TOP}
+
 # Copy all of the include/uapi files to the kernel headers uapi directory.
 copy_hdrs "${KERNEL_DIR}/${src_dir}/include/uapi" "${ANDROID_KERNEL_DIR}/uapi"