scsi: mpt3sas: Replace a dynamic allocation with a local variable

mpt3sas_base.c:_base_update_diag_trigger_pages() allocates and fetches a
MPI2_CONFIG_PAGE_SASIOUNIT_1 struct (Mpi2SasIOUnitPage_t), but does not
include the terminal flexible array member in the struct size calculation,
fetch that member, or otherwise use that member in any way.

This dynamic allocation can be replaced with a local variable.

Signed-off-by: James Seo <james@equiv.tech>
Link: https://lore.kernel.org/r/20230806170604.16143-12-james@equiv.tech


Tested-by: Borislav Petkov (AMD) <bp@alien8.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>