io: io_stm32image: correct possible NULL pointer dereference

This issue was found with cppcheck in our downstream code:
[drivers/st/io/io_stm32image.c:234] -> [drivers/st/io/io_stm32image.c:244]:
 (warning) Either the condition 'buffer!=0U' is redundant or there is
 possible null pointer dereference: local_buffer.

Change-Id: Ieb615b7e485dc93bbeeed4cd8bf845eb84c14ac9
Signed-off-by: Yann Gautier <yann.gautier@st.com>
1 file changed