fs/proc/vmcore.c: use new typedef vm_fault_t

Use new return type vm_fault_t for fault handler in struct
vm_operations_struct.  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.

See 1c8f4220 ("mm: change return type to vm_fault_t") for reference.

Link: http://lkml.kernel.org/r/20180702153325.GA3875@jordon-HP-15-Notebook-PCSigned-off-by: Souptick Joarder <jrdr.linux@gmail.com>
Reviewed-by: Matthew Wilcox <mawilcox@microsoft.com>
Cc: Ganesh Goudar <ganeshgr@chelsio.com>
Cc: Rahul Lakkireddy <rahul.lakkireddy@chelsio.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Alexey Dobriyan <adobriyan@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>

fs/proc/vmcore.c

@@ -379,7 +379,7 @@ static ssize_t read_vmcore(struct file *file, char __user *buffer,
  * On s390 the fault handler is used for memory regions that can't be mapped
  * directly with remap_pfn_range().
  */
-static int mmap_vmcore_fault(struct vm_fault *vmf)
+static vm_fault_t mmap_vmcore_fault(struct vm_fault *vmf)
 {
 #ifdef CONFIG_S390
 	struct address_space *mapping = vmf->vma->vm_file->f_mapping;