event/cnxk: fix clang build on Arm

event/cnxk: fix clang build on Arm

clang-10 build issue log:
drivers/event/cnxk/cnxk_tim_worker.h:372:23:
warning: value size does not match register size
specified by the constraint and modifier [-Wasm-operand-widths]
                             : [rem] "=&r"(rem)
                                           ^
cnxk/cnxk_tim_worker.h:365:17: note: use constraint modifier "w"
                             "ldxr %[rem], [%[crem]]  \n"
                                             ^~~~~~
                                             %w[rem]

Changed variable type to match register size, which placates clang.

Fixes: 300b796262a1 ("event/cnxk: add timer arm routine")
Cc: stable@dpdk.org
Signed-off-by: Ruifeng Wang <ruifeng.wang@arm.com>
Acked-by: Pavan Nikhilesh <pbhagavatula@marvell.com>