Fix deadlock in __hpf()

When erroring out, we were not unlocking first.

As a side note, if you give the kernel a virtual address and tell it to use
it for an operation (e.g. read(fd, VIRT_ADDR, amt), that memory should be
anonymous memory.  At the very least, it must be soft-faultable (i.e.  not
a file that isn't in the page cache).  Considering there's limited control
over that, I currently don't allow that either.  So something like this
will fail:

	va = mmap(..., fd, 0)
	read(another_fd, va, amt);

This restriction is stricter than Linux, and is because of userspace's role
in managing its own memory - it's up to the user to know what is or isn't
resident.

Signed-off-by: Barret Rhoden <brho@cs.berkeley.edu>

kern/src/mm.c

diff --git a/kern/src/mm.c b/kern/src/mm.c
index 91b3d76..906d297 100644
--- a/kern/src/mm.c
+++ b/kern/src/mm.c
@@ -1053,8 +1053,10 @@
 			goto out;
 		}
 	} else {
-		if (!file_ok)
-			return -EACCES;
+		if (!file_ok) {
+			ret = -EACCES;
+			goto out;
+		}
 		/* If this fails, either something got screwed up with the VMR, or the
 		 * permissions changed after mmap/mprotect.  Either way, I want to know
 		 * (though it's not critical). */