mm: page_alloc: Add u64 typecast to memblock_dbg call in free_reserved_area

In 32 bit kernel it is observed that "%#016llx" specifier is not work
properly with return value of __pa().
[    0.649669] Freeing initrd memory: 776K
[    0.649696] memblock_free: [0xc19034a0456ff000-0xc15c615bc199011c] 0xc563d000

To get the proper print with "%#016llx" specifier, __pa() return value is
typecasted with (u64).
[    0.754901] Freeing initrd memory: 776K
[    0.754936] memblock_free: [0x0000004563d000-0x000000456ff000] free_initrd+0x3c/0x60.

Change-Id: I7e84e6c49fefaf3016113b1e547bad0e212a19ed
Signed-off-by: Faiyaz Mohammed <faiyazm@codeaurora.org>