sparc64: fix unused variable warning

sparc64: fix unused variable warning

   arch/sparc/mm/init_64.c: In function 'arch_hugetlb_valid_size':
   arch/sparc/mm/init_64.c:361:24: warning: variable 'hv_pgsz_idx'
     set but not used [-Wunused-but-set-variable]
     361 |         unsigned short hv_pgsz_idx;
         |                        ^~~~~~~~~~~

Reported-by: kernel test robot <lkp@intel.com>
Cc: sparclinux@vger.kernel.org
CC: Nitin Gupta <nitin.m.gupta@oracle.com>
Cc: Andreas Larsson <andreas@gaisler.com>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: Alex Shi <alexs@kernel.org>
Reviewed-by: Andreas Larsson <andreas@gaisler.com>
Signed-off-by: Andreas Larsson <andreas@gaisler.com>