Use new return type vm_fault_t for fault handler.  For now, this is just
documenting that the function returns a VM_FAULT value rather than an
errno.  Once all instances are converted, vm_fault_t will become a
distinct type.

Ref-> 1c8f4220 ("mm: change return type to vm_fault_t")

Previously vm_insert_{pfn,mixed} returns err which driver mapped into
VM_FAULT_* type.  The new function vmf_insert_{pfn,mixed} will replace
this inefficiency by returning VM_FAULT_* type.

vmf_error() is the newly introduce inline function in 4.17-rc6.

Link: http://lkml.kernel.org/r/20180713154541.GA3345@jordon-HP-15-Notebook-PCSigned-off-by: Souptick Joarder <jrdr.linux@gmail.com>
Reviewed-by: Matthew Wilcox <mawilcox@microsoft.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>