Display error if TFTP field empty

If either TFTP Server IP Address or File Name is empty for the
"Download image file from TFTP server" function, return and
display an error.

Tested: Verified I see this error if either field is empty.

Change-Id: I3da3353dad7cfb0f765d8a662412c3adb3fa4efd
Signed-off-by: Gunnar Mills <gmills@us.ibm.com>
diff --git a/app/configuration/controllers/firmware-controller.html b/app/configuration/controllers/firmware-controller.html
index dc85606..c30b4d2 100644
--- a/app/configuration/controllers/firmware-controller.html
+++ b/app/configuration/controllers/firmware-controller.html
@@ -46,6 +46,7 @@
 					</div>
 				</div>
 				<div class="inline uploading" ng-show="downloading">Downloading in progress...</div>
+				<p class="download_error error-msg" ng-show="download_error_msg" role="alert">{{download_error_msg}}</p>
 			</fieldset>
 		</div>
 	</form>