common: seq_read_bench argument order changed

The argument order for seq_read_bench in src/common/obj_bencher.h has
been changed to match the argument order in obj_bencher.cc

Calls to seq_read_bench already use the correct order.
seq_read_bench also matches the order of rand_read_bench and
write_bench

Signed-off-by: Kevin Dalley <kevin@kelphead.org>