mmc: remove redundant irq disabling

There is no need to disable irq's when using the sg_copy_*_buffer()
functions because those functions do that already. There are also
no races for the mm_queue struct here that would require the irq's
to be disabled before calling sg_copy_*_buffer().

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Chris Ball <cjb@laptop.org>