arch/sparc/mm/srmmu.c: fix build

"mm: consolidate pte_index() and pte_offset_*() definitions" was supposed
to remove arch/sparc/mm/srmmu.c:pte_offset_kernel().

Fixes: 974b9b2c ("mm: consolidate pte_index() and pte_offset_*() definitions")
Reported-by: kernel test robot <lkp@intel.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>