input: touchscreen: 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
Signed-off-by: Andrew Chant <achant@google.com>

Change-Id: Ib2b5a53034fd1306d29a74ff0f2f698f149fc8c3
Git-repo: https://android.googlesource.com/kernel/msm


Git-commit: 70e632224737d448b1b4083af7d6b8fcee02b192
Signed-off-by: Dennis Cagle <dcagle@codeaurora.org>
Signed-off-by: Shantanu Jain <shjain@codeaurora.org>