include/linux/dax.h: dax_iomap_fault() returns vm_fault_t

Commit 1c8f4220 ("mm: change return type to vm_fault_t") missed a
conversion.  It's not a big problem at present because mainline is still
using

	typedef int vm_fault_t;

Fixes: 1c8f4220 ("mm: change return type to vm_fault_t")
Link: http://lkml.kernel.org/r/20180620172046.GA27894@jordon-HP-15-Notebook-PC


Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>