drivers/dax/device.c: convert variable to vm_fault_t type

As part of 226ab561075f ("device-dax: Convert to vmf_insert_mixed and
vm_fault_t") in 4.19-rc1, 'rc' was not converted to vm_fault_t. Now
converted.

Link: http://lkml.kernel.org/r/20180830153813.GA26059@jordon-HP-15-Notebook-PC
Signed-off-by: Souptick Joarder <[e-mail]>
Cc: Dan Williams <[e-mail]>
Cc: Dave Jiang <[e-mail]>
Cc: Ross Zwisler <[e-mail]>
Cc: Vishal Verma <[e-mail]>
Cc: Matthew Wilcox <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/dax/device.c

···
 {
 	struct file *filp = vmf->vma->vm_file;
 	unsigned long fault_size;
-	int rc, id;
+	vm_fault_t rc = VM_FAULT_SIGBUS;
+	int id;
 	pfn_t pfn;
 	struct dev_dax *dev_dax = filp->private_data;