dma-buf/sync_file: Don't leak fences on merge failure

Each add_fence() call does a dma_fence_get() on the relevant fence.  In
the error path, we weren't calling dma_fence_put() so all those fences
got leaked.  Also, in the krealloc_array failure case, we weren't
freeing the fences array.  Instead, ensure that i and fences are always
zero-initialized and dma_fence_put() all the fences and kfree(fences) on
every error path.

Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Christian König <christian.koenig@amd.com>
Fixes: a02b9dc9

 ("dma-buf/sync_file: refactor fence storage in struct sync_file")
Cc: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Cc: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210624174732.1754546-1-jason@jlekstrand.net
Signed-off-by: Christian König <christian.koenig@amd.com>