mmc: Fix clock scaling for HS400 with enhanced strobe

Much of the sequence to scale up to HS400 is not required when
enhanced strobe mode for HS400 is supported. Handle scale up
to HS400 appropriately in this case.

Change-Id: I733f98bdb99e54d6cd3a074fcece2c89aaaee12f
Signed-off-by: Venkat Gopalakrishnan <venkatg@codeaurora.org>