staging: vc04_services: fix dmac_map/unmap_area prototypes

You don't define a function prototype on one line as a #define, and then
the next declare it as an external C function, without expecting a C
compiler to complain loudly.

So fix up this mess.

Cc: Daniel Stone <daniels@collabora.com>
Cc: "Noralf Trønnes" <noralf@tronnes.org>
Cc: Pranith Kumar <bobby.prani@gmail.com>
Cc: popcornmix <popcornmix@gmail.com>
Cc: Eric Anholt <eric@anholt.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>