sim: ppc: silence some Wpointer-sign warnings

When compiling with --enable-werror and CFLAGS="-O0 -g -Wall", we run into:
...
src/sim/ppc/hw_memory.c: In function ‘hw_memory_init_address’:
src/sim/ppc/hw_memory.c:204:7: error: pointer targets in passing argument 
4 \
  of ‘device_find_integer_array_property’ differ in signedness \
  [-Werror=pointer-sign]
       &new_chunk->size);
       ^
...

Silence the warnings by adding an explicit pointer cast.  This makes the type
conversion explicit, and doesn't change the current behavior.

This may actually need a proper fix, but that's out of scope for this patch,
which merely aims to fix the build with parameters as used by the openSUSE gdb
package.

---
 sim/ppc/hw_memory.c | 4 ++--
 sim/ppc/hw_opic.c   | 6 ++++--
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/sim/ppc/hw_memory.c b/sim/ppc/hw_memory.c
index 46b22f7b6e3..c0826b71139 100644
--- a/sim/ppc/hw_memory.c
+++ b/sim/ppc/hw_memory.c
@@ -199,9 +199,9 @@ hw_memory_init_address(device *me)
 	 cell_nr += 2) {
       hw_memory_chunk *new_chunk = ZALLOC(hw_memory_chunk);
       device_find_integer_array_property(me, "available", cell_nr,
-					 &new_chunk->address);
+					 (signed_cell *)&new_chunk->address);
       device_find_integer_array_property(me, "available", cell_nr + 1,
-					 &new_chunk->size);
+					 (signed_cell *)&new_chunk->size);
       new_chunk->available = 1;
       *curr_chunk = new_chunk;
       curr_chunk = &new_chunk->next;
diff --git a/sim/ppc/hw_opic.c b/sim/ppc/hw_opic.c
index 8afe312a7ef..9404204aa2f 100644
--- a/sim/ppc/hw_opic.c
+++ b/sim/ppc/hw_opic.c
@@ -417,10 +417,12 @@ hw_opic_init_data(device *me)
       }
       if (!device_find_integer_array_property(me, "interrupt-ranges",
 					      reg_nr * 2,
-					      &opic->isu_block[isb].int_number)
+					      (signed_cell *)
+					        &opic->isu_block[isb].int_number)
 	  || !device_find_integer_array_property(me, "interrupt-ranges",
 						 reg_nr * 2 + 1,
-						 &opic->isu_block[isb].range))
+						 (signed_cell *)
+						   &opic->isu_block[isb].range))
 	device_error(me, "missing or invalid interrupt-ranges property entry %d", reg_nr);
       /* first reg entry specifies the address of both the IDU and the
          first set of ISU registers, adjust things accordingly */