ia64: old_rr4 added under CONFIG_HUGETLB_PAGE

kernel test robot throws below warning ->

arch/ia64/include/asm/mmu_context.h: In function 'reload_context':
   arch/ia64/include/asm/mmu_context.h:127:48: warning: variable
'old_rr4' set but not used [-Wunused-but-set-variable]
     127 |         unsigned long rr0, rr1, rr2, rr3, rr4, old_rr4;

Add it under CONFIG_HUGETLB_PAGE

Link: https://lkml.kernel.org/r/20220626022114.4020-1-jrdr.linux@gmail.com


Signed-off-by: Souptick Joarder (HPE) <jrdr.linux@gmail.com>
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>