cuttlefish launch: fix qemu_gdb flag

Due to an earlier refactoring of the flag code, the parameter passed to
-qemu_gdb was treated as a (relative) path. In that case the example
from the documentation (-qemu_gdb=tcp::1234) was passed as
/your/current/path/tcp::1234.

Restore the original behaviour.

Test: tested in local environment
Change-Id: I38d20b6298de892f22303c19624d587f239af655
Signed-off-by: Matthias Maennich <maennich@google.com>
diff --git a/host/libs/config/cuttlefish_config.cpp b/host/libs/config/cuttlefish_config.cpp
index 1173b1c..1a838b8 100644
--- a/host/libs/config/cuttlefish_config.cpp
+++ b/host/libs/config/cuttlefish_config.cpp
@@ -193,7 +193,7 @@
 }
 
 void CuttlefishConfig::set_gdb_flag(const std::string& device) {
-  SetPath(kGdbFlag, device);
+  (*dictionary_)[kGdbFlag] = device;
 }
 
 std::set<std::string> CuttlefishConfig::kernel_cmdline() const {