dma-buf: Use atomic64_inc_return() in dma_buf_getfile()

Use atomic64_inc_return(&ref) instead of atomic64_add_return(1, &ref)
to use optimized implementation and ease register pressure around
the primitive for targets that implement optimized variant.

Signed-off-by: Uros Bizjak <[e-mail]>
Cc: Sumit Semwal <[e-mail]>
Cc: "Christian König" <[e-mail]>
Signed-off-by: Sumit Semwal <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/dma-buf/dma-buf.c

···
 	 * Override ->i_ino with the unique and dmabuffs specific
 	 * value.
 	 */
-	inode->i_ino = atomic64_add_return(1, &dmabuf_inode);
+	inode->i_ino = atomic64_inc_return(&dmabuf_inode);
 	flags &= O_ACCMODE | O_NONBLOCK;
 	file = alloc_file_pseudo(inode, dma_buf_mnt, "dmabuf",
 				 flags, &dma_buf_fops);