spi: cadence: Fix busy cycles calculation

commit 52b522d7be2e77e8854a47bf0ee1fa6f5702372b from
git@git.assembla.com:cavium/WindRiver.linux.git

If xSPI is in x2/x4/x8 mode to calculate busy
cycles, busy bits count must be divided by the number
of lanes.
If opcommand is using 8 busy bits, but SPI is
in x4 mode, there will be only 2 busy cycles.

Signed-off-by: Witold Sadowski <wsadowski@marvell.com>
Change-Id: I95f42e762e283c360e6369cb00af0ad49f96e603
Reviewed-on: https://sj1git1.cavium.com/c/IP/SW/kernel/linux/+/67406
Tested-by: sa_ip-sw-jenkins <sa_ip-sw-jenkins@marvell.com>
Reviewed-by: Chandrakala Chavva <cchavva@marvell.com>
Reviewed-by: Sunil Kovvuri Goutham <sgoutham@marvell.com>
Signed-off-by: Ruiqiang Hao <Ruiqiang.Hao@windriver.com>