remoteproc/mediatek: fix boundary check

It is valid if offset+length == sram_size.

For example, sram_size=100, offset=99, length=1.  Accessing offset 99
with length 1 is valid.

Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Tzung-Bi Shih <tzungbi@google.com>
Link: https://lore.kernel.org/r/20201116084413.3312631-2-tzungbi@google.com


Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>