openrisc: mm/init.c: remove unused variable 'end' in paging_init()

A build with W=1 enabled produces the following warning:

  CC      arch/openrisc/mm/init.o
arch/openrisc/mm/init.c: In function 'paging_init':
arch/openrisc/mm/init.c:131:16: warning: variable 'end' set but not used [-Wunused-but-set-variable]
  131 |  unsigned long end;
      |                ^~~

Remove the unused variable 'end'.

Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Stafford Horne <shorne@gmail.com>