net: systemport: Fix ordering in intrl2_*_mask_clear macro

Since we keep shadow copies of which interrupt sources are enabled
through the intrl2_*_mask_{set,clear} macros, make sure that the
ordering in which we do these two operations: update the copy, then
unmask the register is correct.

This is not currently a problem because we actually do not use them, but
we will in a subsequent patch optimizing register accesses, so better be
safe here.

Fixes: 80105bef

 ("net: systemport: add Broadcom SYSTEMPORT Ethernet MAC driver")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>