v4.2-rc1 enabled huge page support for ioremap(..).
Calling vmalloc_to_page after v4.2-rc1 results in the
crash shown below on the host upon booting X100 coprocessors:

BUG: unable to handle kernel paging request at ffffc47c00000000
IP: [<ffffffff811a2c0c>] vmalloc_to_page+0x6c/0xb0

This patch fixes this crash by obtaining the fake struct page
pointer which is required to be passed into dma_map_sg(..)
by calling pfn_to_page(..) instead of vmalloc_to_page(..).

Link: https://lkml.org/lkml/2015/7/18/110Reviewed-by: Nikhil Rao <nikhil.rao@intel.com>
Suggested-by: Toshi Kani <toshi.kani@hp.com>
Signed-off-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Signed-off-by: Sudeep Dutt <sudeep.dutt@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>