soc: Fix out of bounds access in register show function

In register show function, when snprintf returns a negative value
out of bounds access occurs while copying the data to user.
Add return value check on snprintf before copy_to_user
to fix this.

Change-Id: I96bfa64b1603c966852c1d4d4a12651664f17aed
Signed-off-by: Aditya Bavanari <abavanar@codeaurora.org>