IB: Fix ib_umem_get() when npages == 0

gcc correctly warned:

drivers/infiniband/core/umem.c: In function 'ib_umem_get':
drivers/infiniband/core/umem.c:78: warning: 'ret' may be used uninitialized in this function

Set ret to 0 in case npages == 0 and the loop isn't entered at all.
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Roland Dreier <rolandd@cisco.com>

drivers/infiniband/core/umem.c

@@ -121,6 +121,7 @@ struct ib_umem *ib_umem_get(struct ib_ucontext *context, unsigned long addr,
 
 	cur_base = addr & PAGE_MASK;
 
+	ret = 0;
 	while (npages) {
 		ret = get_user_pages(current, current->mm, cur_base,
 				     min_t(int, npages,