Staging: vme: Rename VME DMA functions

The DMA resource allocation function is called "vme_request_dma" while
master and slave window allocation functions are called
"vme_master_request" and "vme_slave_request" respectively. Rename
"vme_request_dma" to "vme_dma_request" to fit the pattern.

Signed-off-by: Martyn Welch <martyn.welch@gefanuc.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>