nfc: st21nfca: Remove unnecessary devm_kzalloc() cast

There is no need to use cast for the returned value
from memory allocation functions, so remove the unnecessary cast.

Detected via Coccinelle script:
scripts/coccinelle/api/alloc/alloc_cast.cocci.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>