Boards: st: nucleo_f303re: fix documentation information

Fix Flash size memory  for nucleo_f303re board

Signed-off-by: Fabrice DJIATSA <fabrice.djiatsa-ext@st.com>
diff --git a/boards/st/nucleo_f303re/doc/index.rst b/boards/st/nucleo_f303re/doc/index.rst
index 967079f..743739f 100644
--- a/boards/st/nucleo_f303re/doc/index.rst
+++ b/boards/st/nucleo_f303re/doc/index.rst
@@ -43,7 +43,7 @@
 - ARM |reg| 32-bit Cortex |reg| -M4 CPU with FPU
 - 72 MHz max CPU frequency
 - VDD from 2.0 V to 3.6 V
-- 512 MB Flash
+- 512 KB Flash
 - 64 + 16 KB SRAM
 - RTC
 - Advanced-control Timer