input: synaptics_dsx: add update bounds checks.

Firmware updates contain offsets that are parsed
by the kernel driver.  Ensure all offsets are within
the bounds of the firmware update.

TESTED:
successfully parsed update firmware on device boot.

Bug: 31525965
Bug: 31968442
Change-Id: I074d3f26d33f723a0b239b59ebc3a680d991cdae
Signed-off-by: Andrew Chant <achant@google.com>