drivers:spi:cadence-xspi: Verify clock before operation

commit 5af1c56f483576ca7bb027723fe025dcbcd12481 from
git@git.assembla.com:cavium/WindRiver.linux.git

Verify if correct clock is set before sending STIG command.
Clock config might be changed by other component, without
notyfing kernel.
To fix it, before sending STIG command verify if correct
clock is set, and if not - set it.

Signed-off-by: Witold Sadowski <wsadowski@marvell.com>
Change-Id: Id3b1ffbd1907e285333bf3d9b2e8e96c485ee1a4
Reviewed-on: https://sj1git1.cavium.com/c/IP/SW/kernel/linux/+/91567


Tested-by: sa_ip-sw-jenkins <sa_ip-sw-jenkins@marvell.com>
Reviewed-by: Chandrakala Chavva <cchavva@marvell.com>
Signed-off-by: Wenlin Kang <wenlin.kang@windriver.com>