uml: free LDT state on process exit

The space allocated for a process LDT wasn't being freed when the process
exited.
Signed-off-by: NJeff Dike <jdike@linux.intel.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

arch/um/kernel/skas/mmu.c

@@ -149,4 +149,6 @@ void destroy_context(struct mm_struct *mm)
 		pmd_free((pmd_t *) mmu->last_pmd);
 #endif
 	}
+
+	free_ldt(mmu);
 }