mmc: sdio: avoid spurious calls to interrupt handlers

Commit 06e8935f ("optimized SDIO IRQ handling for single irq")
introduced some spurious calls to SDIO function interrupt handlers,
such as when the SDIO IRQ thread is started, or the safety check
performed upon a system resume.  Let's add a flag to perform the
optimization only when a real interrupt is signaled by the host
driver and we know there is no point confirming it.

Change-Id: Ibfd6b35589b15fabea7b1c18dfa2197a78866b61
Reported-by: Sujit Reddy Thumma <sthumma@codeaurora.org>
Signed-off-by: Nicolas Pitre <nico@linaro.org>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Chris Ball <cjb@laptop.org>
Signed-off-by: Sujit Reddy Thumma <sthumma@codeaurora.org>