mmc: of_mmc_spi: add NO_IRQ define to of_mmc_spi.c

Provide a dummy value of NO_IRQ for architectures that don't support
it (such as MIPS).  Fixes the build error for MIPS.

Signed-off-by: Wanlong Gao <wanlong.gao@gmail.com>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Chris Ball <cjb@laptop.org>