powerpc/85xx: Fix signedness bug in cache-sram

sram_params.sram_size and sram_params.sram_offset were unsigned.
If get_cache_sram_size() or get_cache_sram_offset() returns error code
then it is not seen to the caller.  Made sram_size and sram_offset signed.
Signed-off-by: Vasiliy Kulikov <segooon@gmail.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>

arch/powerpc/sysdev/fsl_85xx_l2ctlr.c

@@ -94,14 +94,14 @@ static int __devinit mpc85xx_l2ctlr_of_probe(struct platform_device *dev,
 	l2cache_size = *prop;
 
 	sram_params.sram_size  = get_cache_sram_size();
-	if (sram_params.sram_size <= 0) {
+	if ((int)sram_params.sram_size <= 0) {
 		dev_err(&dev->dev,
 			"Entire L2 as cache, Aborting Cache-SRAM stuff\n");
 		return -EINVAL;
 	}
 
 	sram_params.sram_offset  = get_cache_sram_offset();
-	if (sram_params.sram_offset <= 0) {
+	if ((int64_t)sram_params.sram_offset <= 0) {
 		dev_err(&dev->dev,
 			"Entire L2 as cache, provide a valid sram offset\n");
 		return -EINVAL;