staging: mt7621-mmc: Remove redundant opcode check

The opcode check in msdc_command_start is redundant in case of
MMC_SET_RELATIVE_ADDR, this is 3 like SD_SEND_RELATIVE_ADDR, so the
second check can be removed.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Christian Lütke-Stetzkamp <christian@lkamp.de>
Reviewed-by: NeilBrown <neil@brown.name>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>