zram01.sh: Increase timeout for check_read_mem_used_total

Increase timeout value to let case pass on low resource ppc64le machine:

zram01 7 TINFO: /sys/block/zram5/mm_stat
11796480        0        0 26214400   196608      180        0        0
zram01 7 TBROK: "check_read_mem_used_total /sys/block/zram5/mm_stat" timed out

Link: https://lore.kernel.org/ltp/[email protected]/
Reviewed-by: Petr Vorel <[email protected]>
Signed-off-by: Wei Gao <[email protected]>

Author: coolgw

testcases/kernel/device-drivers/zram/zram01.sh

@@ -155,7 +155,7 @@ zram_fill_fs()
 			continue
 		fi
 
-		TST_RETRY_FUNC "check_read_mem_used_total /sys/block/zram$i/mm_stat" 0
+		TST_RETRY_FN_EXP_BACKOFF "check_read_mem_used_total /sys/block/zram$i/mm_stat" 0 10
 		mem_used_total=$(read_mem_used_total /sys/block/zram$i/mm_stat)
 		tst_res TINFO "mem_used_total: $mem_used_total"