mmc: core: check if manual BKOPS is ongoing before scaling

Clock scaling commands are not allowed to be sent when the device
performs manual BKOPS.
In case the device is busy with manual BKOPS, skip the clock
scaling and allow the device to continue the BKOPS.
Clock scaling will be invoked again later by dev freq.

Change-Id: I78b505326d245b1ddcd9d6f1cdd4294850889d45
Signed-off-by: Maya Erez <merez@codeaurora.org>