[dv] Cleanup lint warnings in uart_agent_pkg

Signed-off-by: Srikrishna Iyer <sriyer@google.com>
diff --git a/hw/dv/sv/uart_agent/uart_agent_pkg.sv b/hw/dv/sv/uart_agent/uart_agent_pkg.sv
index 12ddb48..1ccb6ba 100644
--- a/hw/dv/sv/uart_agent/uart_agent_pkg.sv
+++ b/hw/dv/sv/uart_agent/uart_agent_pkg.sv
@@ -45,6 +45,7 @@
       BaudRate230400: return 4340.278;
       BaudRate1Mbps : return 953.674;
       BaudRate2Mbps : return 476.837;
+      default: `uvm_fatal("uart_agent_pkg", {"Unsupported baud_rate: ", baud_rate.name})
     endcase
   endfunction