dma-buf/resv: fix exclusive fence get

This causes kernel crash when testing lima driver.

Cc: Christian König <[e-mail]>
Fixes: b8c036dfc66f ("dma-buf: simplify reservation_object_get_fences_rcu a bit")
Signed-off-by: Qiang Yu <[e-mail]>
Reviewed-by: Chris Wilson <[e-mail]>
Signed-off-by: Chris Wilson <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/dma-buf/dma-resv.c

···
 	if (pfence_excl)
 		*pfence_excl = fence_excl;
 	else if (fence_excl)
-		shared[++shared_count] = fence_excl;
+		shared[shared_count++] = fence_excl;
 
 	if (!shared_count) {
 		kfree(shared);