gdbserver/proc-service.c: Change CORE_ADDR cast to uintptr_t

gdbserver/proc-service.c: Change CORE_ADDR cast to uintptr_t

Fixes on i386:

../../../binutils-gdb/gdb/gdbserver/proc-service.c: In function ps_pdread:
../../../binutils-gdb/gdb/gdbserver/proc-service.c:83:25: error: cast from pointer to integer of different size [-Werror=pointer-to-int-cast]
../../../binutils-gdb/gdb/gdbserver/proc-service.c: In function ps_pdwrite:
../../../binutils-gdb/gdb/gdbserver/proc-service.c:93:30: error: cast from pointer to integer of different size [-Werror=pointer-to-int-cast]

I could have kept both casts:

  (CORE_ADDR) (uintptr_t) addr

but it's cleaner this way.  The uintptr_t implicitely gets promoted to a
CORE_ADDR, which is at least as long as uintptr_t.

gdb/gdbserver/ChangeLog:

	* proc-service.c (ps_pdread): Change CORE_ADDR cast to uintptr_t.
	(ps_pdwrite): Likewise.