rtc: pxa: fix probe function

This patch is from static analysis and I don't have the hardware to
to test it.  I think the test is reversed so now the probe function
will return success early and the last part of the function is dead
code.

Fixes: 3cdf4ad9 ("rtc: pxa: convert to use shared sa1100 functions")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>