mmc: mmc_spi: Read R2 response for send status command - CMD13

Send status command (CMD13) will send R1 response under SD mode
but R2 response under SPI mode.

R2 response is 2 bytes long, so read 2 bytes for mmc SPI mode

Signed-off-by: Pragnesh Patel <pragnesh.patel@sifive.com>
Reviewed-by: Bin Meng <bin.meng@windriver.com>
Tested-by: Bin Meng <bin.meng@windriver.com>