Fix product model in init.espresso.rc

I don't know if this needs to just be GT-P3100
for both the 3100 and 3110 or if we can use a variable
like I have it now, also if someone can tell me if the
variable is correct or the $ needs to go inside the brackets
if we need to differentiate.

Change-Id: I7f9a8c973e4cace45aa470701354afdd1cef6279