selftests/vm/pkeys: fix typo in comment

Spelling mistake (triple letters) in comment.  Detected with the help of
Coccinelle.

Link: https://lkml.kernel.org/r/20220521111145.81697-80-Julia.Lawall@inria.fr
Signed-off-by: Julia Lawall <Julia.Lawall@inria.fr>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: JuliaLawall

tools/testing/selftests/vm/protection_keys.c

@@ -1523,7 +1523,7 @@ void test_implicit_mprotect_exec_only_memory(int *ptr, u16 pkey)
 	/*
 	 * Reset the shadow, assuming that the above mprotect()
 	 * correctly changed PKRU, but to an unknown value since
-	 * the actual alllocated pkey is unknown.
+	 * the actual allocated pkey is unknown.
 	 */
 	shadow_pkey_reg = __read_pkey_reg();