Fixes vb2_vmalloc_get_userptr() to ioremap correct area.
Since the current code does ioremap the page address, if the offset > 0,
it does not do ioremap the last page and results in kernel panic.
This fixes to pass the size + offset to ioremap so that ioremap
can map correct area. Also, this uses __pfn_to_phys() to get the physical
address of given PFN.