Fix adb_gdb script.

Fix a typo in the script.
BUG=304931
R=digit@chromium.org

Review URL: https://codereview.chromium.org/26337002

git-svn-id: http://src.chromium.org/svn/trunk/src/build@227340 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

android/adb_gdb

@@ -547,7 +547,7 @@ ANDROID_TOOLCHAIN=${ANDROID_TOOLCHAIN%/}
 # Find host GDB client binary
 if [ -z "$GDB" ]; then
   GDB=$(which $ANDROID_TOOLCHAIN/*-$GDBEXEPOSTFIX 2>/dev/null | head -1)
-  if [ -z "$GDBSERVER" ]; then
+  if [ -z "$GDB" ]; then
     panic "Can't find Android gdb client in your path, check your \
 --toolchain or --gdb path."
   fi