gpu: nvgpu: posix: make round*_pow_of_two CERT-C friendly

CERT-C Rule INT30 requires checking unsigned arithmetic for potential
wrap. The macros roundup_pow_of_two and rounddown_pow_of_two could
potentially wrap if the passed parameter were 0.

JIRA NVGPU-3586

Change-Id: I9eba4c197b74db555055e1199ce72131b071062c
Signed-off-by: Philip Elcan <pelcan@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/2131157
GVS: Gerrit_Virtual_Submit
Reviewed-by: Nitin Kumbhar <nkumbhar@nvidia.com>
Reviewed-by: mobile promotions <svcmobile_promotions@nvidia.com>
Tested-by: mobile promotions <svcmobile_promotions@nvidia.com>

drivers/gpu/nvgpu/include/nvgpu/posix/log2.h

@@ -33,8 +33,29 @@
 				fls_val;			\
 			})
 
-#define roundup_pow_of_two(x)		(1UL << fls((x) - 1UL))
+#define roundup_pow_of_two(x)						\
-#define rounddown_pow_of_two(x)		(1UL << (fls(x) - 1UL))
+			({						\
+				unsigned long ret;			\
+									\
+				if ((x) == 0UL) {			\
+					BUG();				\
+				} else {				\
+					ret = 1UL << fls((x) - 1UL);	\
+				}					\
+				ret;					\
+			})
+
+#define rounddown_pow_of_two(x)						\
+			({						\
+				unsigned long ret;			\
+									\
+				if ((x) == 0UL) {			\
+					BUG();				\
+				} else {				\
+					ret = 1UL << (fls(x) - 1UL);	\
+				}					\
+				ret;					\
+			})
 
 #define is_power_of_2(x)					\
 	(bool)({						\