gdb/riscv: Fix type when reading register from regcache

Should use a ULONGEST when reading from the regcache.

gdb/ChangeLog:

	* riscv-tdep.c (riscv_return_value): Change type to ULONGEST for
	reading values from registers.

gdb/ChangeLog

@@ -1,3 +1,8 @@
+2018-03-06  Andrew Burgess  <andrew.burgess@embecosm.com>
+
+	* riscv-tdep.c (riscv_return_value): Change type to ULONGEST for
+	reading values from registers.
+
 2018-03-06  Andrew Burgess  <andrew.burgess@embecosm.com>
 
 	* riscv-tdep.c (riscv_push_dummy_call): Use core_addr_to_string_nz

gdb/riscv-tdep.c

@@ -2318,7 +2318,7 @@ riscv_return_value (struct gdbarch  *gdbarch,
 	    /* Return value by reference will have its address in A0.  */
 	  case riscv_arg_info::location::by_ref:
 	    {
-	      CORE_ADDR addr;
+	      ULONGEST addr;
 
 	      regcache_cooked_read_unsigned (regcache, RISCV_A0_REGNUM,
 					     &addr);