nfc: pn533: remove redundant assignment

In many places,first assign a value to a variable and then return
the variable. which is redundant, we should directly return the value.
in pn533_rf_field funciton,return rc also in the if statement, so we
use return 0 to replace the last return rc.

Signed-off-by: wengjianfeng <wengjianfeng@yulong.com>
Signed-off-by: David S. Miller <davem@davemloft.net>