target/ast10x0: fix gpio test RAM size issue.

target/ast10x0/tests/peripherals/gpio/gpio_smoke/system.json5

diff --git a/target/ast10x0/tests/peripherals/gpio/gpio_smoke/system.json5 b/target/ast10x0/tests/peripherals/gpio/gpio_smoke/system.json5
index 501a700..42ae443 100644
--- a/target/ast10x0/tests/peripherals/gpio/gpio_smoke/system.json5
+++ b/target/ast10x0/tests/peripherals/gpio/gpio_smoke/system.json5
@@ -12,6 +12,6 @@
         flash_start_address: 0x00000500,
         flash_size_bytes: 262144,
         ram_start_address: 0x00040500,
-        ram_size_bytes: 393216,
+        ram_size_bytes: 391936, // ends at RAM_NC boundary (0x000A0000)
     },
 }