staging: mt7621-mmc: Remove unnecessary BUG_ON() in msdc_dma_setup

The BUG_ON() removed by this patch is just a duplicate of a prior
BUG_ON() statement. There the condition is just clearer, it checks
weather sglen > MAX_BD_NUM and MAX_BD_NUM is equal MAX_BD_PER_GPD. So
this statement can be safely removed.

Signed-off-by: Christian Lütke-Stetzkamp <christian@lkamp.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>