[PATCH] gpu: drm: gma500: Change return type to vm_fault_t

[Souptick Joarder]

>>> drivers/gpu/drm/gma500/framebuffer.c:136:9: error: implicit declaration of function 'vmf_insert_mixed'; did you mean 'vm_insert_mixed'? [-Werror=implicit-function-declaration]
>       ret = vmf_insert_mixed(vma, address,
>             ^~~~~~~~~~~~~~~~
>    cc1: some warnings being treated as errors
> --


>>> drivers/gpu/drm/gma500/gem.c:165:10: error: implicit declaration of function 'vmf_error' [-Werror=implicit-function-declaration]
>        ret = vmf_error(err);

Sorry about it. vmf_error() is not yet merged in linus tree and
it break the build.

>>> drivers/gpu/drm/gma500/gem.c:180:8: error: implicit declaration of function 'vmf_insert_pfn'; did you mean 'vm_insert_pfn'? [-Werror=implicit-function-declaration]
>      ret = vmf_insert_pfn(vma, vmf->address, pfn);

               vm_insert_mixed() , vmf_insert_pfn() is defined in <linux/mm.h>
               and vm_fault_t is defined in vm_fault_t in <linux/mm_types.h>
               and merged in both 4.17-rc1 and next-20180413.
               So these shouldn't break the build.