x86/mm/pkeys: Fix typo in Documentation/x86/protection-keys.txt

Replace PKEY_DENY_WRITE with PKEY_DISABLE_WRITE,
to match the source code.

Signed-off-by: Wang Kai <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Signed-off-by: Ingo Molnar <[e-mail]>

Documentation/x86/protection-keys.txt

···
 called pkey_set().
 
 	int real_prot = PROT_READ|PROT_WRITE;
-	pkey = pkey_alloc(0, PKEY_DENY_WRITE);
+	pkey = pkey_alloc(0, PKEY_DISABLE_WRITE);
 	ptr = mmap(NULL, PAGE_SIZE, PROT_NONE, MAP_ANONYMOUS|MAP_PRIVATE, -1, 0);
 	ret = pkey_mprotect(ptr, PAGE_SIZE, real_prot, pkey);
 	... application runs here
···
 Now, if the application needs to update the data at 'ptr', it can
 gain access, do the update, then remove its write access:
 
-	pkey_set(pkey, 0); // clear PKEY_DENY_WRITE
+	pkey_set(pkey, 0); // clear PKEY_DISABLE_WRITE
 	*ptr = foo; // assign something
-	pkey_set(pkey, PKEY_DENY_WRITE); // set PKEY_DENY_WRITE again
+	pkey_set(pkey, PKEY_DISABLE_WRITE); // set PKEY_DISABLE_WRITE again
 
 Now when it frees the memory, it will also free the pkey since it
 is no longer in use: