UPSTREAM: i2c: ismt: prevent memory corruption in ismt_access()

commit 690b2549 upstream.

The "data->block[0]" variable comes from the user and is a number
between 0-255.  It needs to be capped to prevent writing beyond the end
of dma_buffer[].

Bug: 247008437
Fixes: 5e9a97b1 ("i2c: ismt: Adding support for I2C_SMBUS_BLOCK_PROC_CALL")
Reported-and-tested-by: Zheyu Ma <zheyuma97@gmail.com>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Lee Jones <joneslee@google.com>
Change-Id: I16cefa30f259ccd57147ff1d3e9747c36e3ed5f9