misc: fastrpc: fix incorrect usage of dma_map_sgtable

dma_map_sgtable() returns 0 on success, which is the opposite of what this
code was doing.

Fixes: 7cd7edb8 ("misc: fastrpc: fix common struct sg_table related issues")
Acked-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Jonathan Marek <jonathan@marek.ca>
Link: https://lore.kernel.org/r/20210208200401.31100-1-jonathan@marek.ca


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>