mmc_spi: generate response for send status command

A "send status" command is added with the commit "mmc: checking
status after commands with R1b response". But the status register
returned from send status command of SPI protocol is different from
that of MMC/SD protocol. We do a simple test and generate a response
in stead of full bit-by-bit translation.

Signed-off-by: Thomas Chou <thomas@wytron.com.tw>