net: dsa: bcm_sf2: cleanup bcm_sf2_cfp_rule_get() a little

This patch doesn't affect how the code works.

My static checker complains that the mask and shift doesn't make sense
because 0xffffff << 16 goes beyond the end of 32 bits.  It should be
0xffff instead but the existing code won't cause runtime bugs.

Also the casting here is not needed and not consistent with the rest of
the code.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>