dma-buf: refactor dma-buf name

rename 'name' to 'buf_name' in dma_buf since 'name' will be used
by the user specified name in upstream commit
"UPSTREAM: dma-buf: add DMA_BUF_SET_NAME ioctls".

Change-Id: I70e20bdb71e964d1da240b1d0323b26bb89d0ddc
Signed-off-by: Srinivasarao P <spathi@codeaurora.org>