dma-debug: fix ia64 build, use PHYS_PFN

kbuild test robot reports:

   lib/dma-debug.c: In function 'debug_dma_map_resource':
>> lib/dma-debug.c:1541:16: error: implicit declaration of function '__phys_to_pfn' [-Werror=implicit-function-declaration]
     entry->pfn  = __phys_to_pfn(addr);
                   ^~~~~~~~~~~~~

ia64 does not provide __phys_to_pfn(), use the PHYS_PFN() alias.

Fixes: 0e74b34d ("dma-debug: add support for resource mappings")
Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>