mmc: queue: Don't peek requests when queue is stopped

Make sure we don't peek the block layer queue and act on it when
block queue is stopped. The block queue will be stopped when mmc
block is suspended, wait till it is properly resumed before pulling
new requests.

Change-Id: Ifc369687c13dae904271e8f92d3604edbd667d82
Signed-off-by: Venkat Gopalakrishnan <venkatg@codeaurora.org>