input: synaptics_dsx: validate bounds of intr_reg_num

Validate the intr_reg_num value returned by touchscreen
to ensure no out of bounds access can occur.

Bug: 35472278
Change-Id: I22f5b67815fe7d448b5ed847e4e3d65af63bed84
Signed-off-by: Andrew Chant <achant@google.com>
Git-repo: https://android.googlesource.com/kernel/msm


Git-commit: 271baca849983ef309e82a4e5953027790f36154
Signed-off-by: Dennis Cagle <dcagle@codeaurora.org>
Signed-off-by: Shantanu Jain <shjain@qti.qualcomm.com>