Replace long int * cast with PTRACE_TYPE_RET *

Replace long int * cast with PTRACE_TYPE_RET *

These casts uses the typedef target type (long int *) instead of the
typedef name.  This was a little mistake in one of the big C++ cast
patches.

gdb/ChangeLog:

	* inf-ptrace.c (inf_ptrace_fetch_register): Change long int *
	cast to PTRACE_TYPE_RET *.
	(inf_ptrace_store_register): Likewise.