staging: sb105x: clean up interface type test

IIR_RS232 is zero so "if (IIR_RS232 == (b_ret & IIR_RS232))" is always
true so RS232 was always chosen by default.  The test should be
"if (0 == (b_ret & 0x30)) { ".  The other tests should also be in that
format.

This does change how the code works...  If 0x30 is set then it now
defaults to RS232 instead of RS485.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>