configure.ac: Fix error message in radeon_llvm_check().

It printed the version of LLVM ($1):

   configure: error: 3.6.0 requires libelf when using llvm

instead of the driver name ($2):

   configure: error: r600 requires libelf when using llvm

Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Tobias Droste <tdroste@gmx.de>

configure.ac

@@ -1013,7 +1013,7 @@ radeon_llvm_check() {
     llvm_add_component "ipo" $2
 
     if test "x$have_libelf" != xyes; then
-       AC_MSG_ERROR([$1 requires libelf when using llvm])
+       AC_MSG_ERROR([$2 requires libelf when using llvm])
     fi
 }