driver core: fix dma-buf.c kernel-doc warnings

Fix kernel-doc warnings in dma-buf.c:

Warning(drivers/base/dma-buf.c:305): No description found for parameter 'dmabuf'
Warning(drivers/base/dma-buf.c:305): Excess function parameter 'dma_buf' description in 'dma_buf_begin_cpu_access'
Warning(drivers/base/dma-buf.c:332): No description found for parameter 'dmabuf'
Warning(drivers/base/dma-buf.c:332): Excess function parameter 'dma_buf' description in 'dma_buf_end_cpu_access'
Warning(drivers/base/dma-buf.c:350): No description found for parameter 'dmabuf'
Warning(drivers/base/dma-buf.c:350): Excess function parameter 'dma_buf' description in 'dma_buf_kmap_atomic'
Warning(drivers/base/dma-buf.c:367): No description found for parameter 'dmabuf'
Warning(drivers/base/dma-buf.c:367): Excess function parameter 'dma_buf' description in 'dma_buf_kunmap_atomic'
Warning(drivers/base/dma-buf.c:385): No description found for parameter 'dmabuf'
Warning(drivers/base/dma-buf.c:385): Excess function parameter 'dma_buf' description in 'dma_buf_kmap'
Warning(drivers/base/dma-buf.c:402): No description found for parameter 'dmabuf'
Warning(drivers/base/dma-buf.c:402): Excess function parameter 'dma_buf' description in 'dma_buf_kunmap'

Signed-off-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>