posix: shm: fix build error with minimal libc

In `lib/posix/options/shm.c` we don't include stdio.h
header but use standard SEEK_xxx definitions (i.e. `SEEK_SET`)
which cause build issues (if the minimal libc is used).

Fix that.

Signed-off-by: Evgeniy Paltsev <PaltsevEvgeniy@gmail.com>
Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>

lib/posix/options/shm.c

@@ -5,6 +5,7 @@
  */
 
 #include <string.h>
+#include <stdio.h>
 
 #include <kernel_arch_interface.h>
 #include <zephyr/kernel.h>