powerpc/boot: Handle allocation failure in simple_realloc()

simple_malloc() will return NULL when there is not enough memory left.
Check pointer 'new' before using it to copy the old data.
Signed-off-by: Li zeming <zeming@nfschina.com>
[mpe: Reword subject, use change log from Christophe]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20221219021816.3012-1-zeming@nfschina.com

arch/powerpc/boot/simple_alloc.c

@@ -112,7 +112,9 @@ static void *simple_realloc(void *ptr, unsigned long size)
 		return ptr;
 
 	new = simple_malloc(size);
+	if (new)
 		memcpy(new, ptr, p->size);
+
 	simple_free(ptr);
 	return new;
 }