powerpc/kexec: fix minor typo

Function name in the descriptor was not correct.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202307251721.bUGcsCeQ-lkp@intel.com/


Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230725132759.53975-1-ldufour@linux.ibm.com