dma-buf: heaps: Remove redundant heap identifier from system heap name

The heaps are already in a directory of heaps, adding _heap to a heap
name is redundant. This patch is only a name change, no logic is changed.

Signed-off-by: Andrew F. Davis <afd@ti.com>
Acked-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20191216133405.1001-3-afd@ti.com