FindDevIL: fail properly when library is not found.

Due to a mismatch between module name and name passed to FPHSA() the
macro printed an error message but the error was not caught up by CMake.
Fix the typo.

Modules/FindDevIL.cmake

@@ -67,6 +67,6 @@ find_library(ILU_LIBRARIES
 
 #message("ILU_LIBRARIES is ${ILU_LIBRARIES}")
 
-FIND_PACKAGE_HANDLE_STANDARD_ARGS(IL DEFAULT_MSG
+FIND_PACKAGE_HANDLE_STANDARD_ARGS(DevIL DEFAULT_MSG
                                   IL_LIBRARIES ILU_LIBRARIES
                                   ILUT_LIBRARIES IL_INCLUDE_DIR)