Fix bug in xrefinfo_find() for 64-bit platforms

uintptr_t may be 64-bit on some platforms, therefore when
finding xrefinfo by pointer to device the high word is being
cut off due to cast to phandle_t which is 32-bit long by definition.
Due to that we loose the high word of the address to compare with
xi->dev's address.
To fix that, first argument of xrefinfo_find() is extended to
uintptr_t and is being cast to appropriate type (phandle_t)
when compared.

Submitted by: Zbigniew Bodek <zbb@semihalf.com>
Reviewed by: nwhitehorn
Obtained from: Semihalf