memstick: make enable_dma less generic in r592

memstick: make enable_dma less generic in r592

Fixes this build error:

  drivers/memstick/host/r592.c:26: error: 'enable_dma' redeclared as different kind of symbol
  arch/powerpc/include/asm/dma.h:189: note: previous definition of 'enable_dma' was here

Signed-off-by: Stephen Rothwell <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: FUJITA Tomonori <[email protected]>
Cc: Alex Dubov <[email protected]>
Acked-by: Maxim Levitsky <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>