ARM: 8426/1: dma-mapping: add missing range check in dma_mmap()

dma_mmap() function in IOMMU-based dma-mapping implementation lacked
a check for valid range of mmap parameters (offset and buffer size), what
might have caused access beyond the allocated buffer. This patch fixes
this issue.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: stable@vger.kernel.org  # v3.6+
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>