Summary:
fix warning
In function 'memorystress_iter',
inlined from 'memstress_main' at memorystress_main.c:475:10:
memorystress_main.c:289:10: error: 'ptr' may be used uninitialized [-Werror=maybe-uninitialized]
289 | if (ptr == NULL)
| ^
memorystress_main.c: In function 'memstress_main':
memorystress_main.c:248:20: note: 'ptr' was declared here
248 | FAR uint8_t *ptr;
| ^~~
Signed-off-by: chenrun1 <chenrun1@xiaomi.com>
