extable: Consolidate *kernel_text_address() functions

The functionality between kernel_text_address() and _kernel_text_address()
is the same except that _kernel_text_address() does a little more (that
function needs a rename, but that can be done another time). Instead of
having duplicate code in both, simply have _kernel_text_address() calls
kernel_text_address() instead.

This is marked for stable because there's an RCU bug that can happen if
one of these functions gets called while RCU is not watching. That fix
depends on this fix to keep from having to write the fix twice.

Cc: stable@vger.kernel.org
Fixes: 0be964be ("module: Sanitize RCU usage and locking")
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>