rt2800pci: Fix compiler error on PowerPC

Using gcc 4.4.5 on a Powerbook G4 with a PPC cpu, a complicated
if statement results in incorrect flow, whereas the equivalent switch
statement works correctly.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Cc: stable <stable@kernel.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>