Silence static analyzer warnings about spa_sync_props()

Both Coverity and Clang's static analyzer complain about reading an
uninitialized intval if the property is not passed as DATA_TYPE_UINT64
in the nvlist. This is impossible becuase spa_prop_validate() already
checked this, but they are unlikely to be the last static analyzers to
complain about this, so lets just refactor the code to suppress the
warnings.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Richard Yao <richard.yao@alumni.stonybrook.edu>
Closes openzfs#14043

module/zfs/spa.c

@@ -8869,36 +8869,36 @@ spa_sync_props(void *arg, dmu_tx_t *tx)
 				spa_history_log_internal(spa, "set", tx,
 				    "%s=%lld", nvpair_name(elem),
 				    (longlong_t)intval);
-			} else {
-				ASSERT(0); /* not allowed */
-			}
 
-			switch (prop) {
-			case ZPOOL_PROP_DELEGATION:
-				spa->spa_delegation = intval;
-				break;
-			case ZPOOL_PROP_BOOTFS:
-				spa->spa_bootfs = intval;
-				break;
-			case ZPOOL_PROP_FAILUREMODE:
-				spa->spa_failmode = intval;
-				break;
-			case ZPOOL_PROP_AUTOTRIM:
-				spa->spa_autotrim = intval;
-				spa_async_request(spa,
-				    SPA_ASYNC_AUTOTRIM_RESTART);
-				break;
-			case ZPOOL_PROP_AUTOEXPAND:
-				spa->spa_autoexpand = intval;
-				if (tx->tx_txg != TXG_INITIAL)
+				switch (prop) {
+				case ZPOOL_PROP_DELEGATION:
+					spa->spa_delegation = intval;
+					break;
+				case ZPOOL_PROP_BOOTFS:
+					spa->spa_bootfs = intval;
+					break;
+				case ZPOOL_PROP_FAILUREMODE:
+					spa->spa_failmode = intval;
+					break;
+				case ZPOOL_PROP_AUTOTRIM:
+					spa->spa_autotrim = intval;
 					spa_async_request(spa,
-					    SPA_ASYNC_AUTOEXPAND);
-				break;
-			case ZPOOL_PROP_MULTIHOST:
-				spa->spa_multihost = intval;
-				break;
-			default:
-				break;
+					    SPA_ASYNC_AUTOTRIM_RESTART);
+					break;
+				case ZPOOL_PROP_AUTOEXPAND:
+					spa->spa_autoexpand = intval;
+					if (tx->tx_txg != TXG_INITIAL)
+						spa_async_request(spa,
+						    SPA_ASYNC_AUTOEXPAND);
+					break;
+				case ZPOOL_PROP_MULTIHOST:
+					spa->spa_multihost = intval;
+					break;
+				default:
+					break;
+				}
+			} else {
+				ASSERT(0); /* not allowed */
 			}
 		}