nfc: st-nci: Remove unnecessary variable

The variable r is defined at the beginning and initialized
to 0 until the function returns r, and the variable r is
not reassigned.Therefore, we do not need to define the
variable r, just return 0 directly at the end of the function.

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