NFC: st21nfca: Convert to use devm_gpio_request_one

This simplifies the code a bit.

Acked-by: Christophe RICARD <christophe-h.ricard@st.com>
Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>