Fix: mm: create the new vm_fault_t type (v5.1)

Fix: mm: create the new vm_fault_t type (v5.1)

See upstream commit:

  commit 3d3539018d2cbd12e5af4a132636ee7fd8d43ef0
  Author: Souptick Joarder <jrdr.linux@gmail.com>
  Date:   Thu Mar 7 16:31:14 2019 -0800

    mm: create the new vm_fault_t type

    Page fault handlers are supposed to return VM_FAULT codes, but some
    drivers/file systems mistakenly return error numbers.  Now that all
    drivers/file systems have been converted to use the vm_fault_t return
    type, change the type definition to no longer be compatible with 'int'.
    By making it an unsigned int, the function prototype becomes
    incompatible with a function which returns int.  Sparse will detect any
    attempts to return a value which is not a VM_FAULT code.

    VM_FAULT_SET_HINDEX and VM_FAULT_GET_HINDEX values are changed to avoid
    conflict with other VM_FAULT codes.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>