isdn: don't mark kcapi_proc_exit as __exit

As everybody pointed out by now, my patch to clean up CAPI introduced
a link time warning, as the two parts of the capi driver are now in
one module and the exit function may need to be called in the error
path of the init function:

>> WARNING: drivers/isdn/capi/kernelcapi.o(.text+0xea4): Section mismatch in reference from the function kcapi_exit() to the function .exit.text:kcapi_proc_exit()
   The function kcapi_exit() references a function in an exit section.
   Often the function kcapi_proc_exit() has valid usage outside the exit section
   and the fix is to remove the __exit annotation of kcapi_proc_exit.

Remove the incorrect __exit annotation.
Reported-by: kbuild test robot <lkp@intel.com>
Reported-by: kernelci.org bot <bot@kernelci.org>
Reported-by: Olof's autobuilder <build@lixom.net>
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20191216194909.1983639-1-arnd@arndb.deSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/isdn/capi/kcapi_proc.c

@@ -217,7 +217,7 @@ kcapi_proc_init(void)
 	proc_create("capi/driver",           0, NULL, &empty_fops);
 }
 
-void __exit
+void
 kcapi_proc_exit(void)
 {
 	remove_proc_entry("capi/driver",       NULL);