liquidio: remove redundant setting of inst_processed to zero

The zero value assigned to inst_processed at the end of each
iteration of the do-while loop is overwritten on the next iteration
and hence it is a redundant assignment and can be removed. Cleans
up clang warning:

drivers/net/ethernet/cavium/liquidio/request_manager.c:480:3:
warning: Value stored to 'inst_processed' is never read

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: David S. Miller <davem@davemloft.net>