Fix user-visible spelling error

Pavel Machek reports a warning about W+X pages found in the "Persisent"
kmap area.  After grepping for it (using the correct spelling), and not
finding it, I noticed how the debug printk was just misspelled.  Fix it.

The actual mapping bug that Pavel reported is still open.  It's
apparently a separate issue from the known EFI page tables, looks like
it's related to the HIGHMEM mappings.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>