configure.ac: fix EOL garbage

Added accidentaly by the commit 73572e7 (2024-03-05). Effective only
if --with-cuda option used but without any implications - just `/FOUN:
not found` printed, but processed normally.

configure.ac

@@ -471,7 +471,7 @@ AC_ARG_ENABLE(cuda,
               [cuda_req=$build_default])
 
 AC_ARG_WITH(cuda,
-            [  --with-cuda=DIR         specify location of CUDA Toolkit],/FOUN
+            [  --with-cuda=DIR         specify location of CUDA Toolkit],
             [CUDA_PATH=$withval
             ])