ARM: shmobile: rcar-gen2: update call to dma_contiguous_reserve_area

Commit 5ea3b1b2 'cma: add placement specifier for "cma=" kernel parameter'
adds a new 'fixed' parameter to dma_contiguous_reserve_area(). Update
rcar_gen2_reserve() accordingly.

This fixes the following compilation error:

  arch/arm/mach-shmobile/setup-rcar-gen2.c: In function ‘rcar_gen2_reserve’:
  arch/arm/mach-shmobile/setup-rcar-gen2.c:182:10: error: too few arguments to function ‘dma_contiguous_reserve_area’

Signed-off-by: Vincent Stehlé <vincent.stehle@laposte.net>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>