NFC: fdp: Detect errors from fdp_nci_create_conn()

drivers/nfc/fdp/fdp.c: In function ‘fdp_nci_patch_otp’:
drivers/nfc/fdp/fdp.c:373: warning: comparison is always false due to limited range of data type
drivers/nfc/fdp/fdp.c: In function ‘fdp_nci_patch_ram’:
drivers/nfc/fdp/fdp.c:444: warning: comparison is always false due to limited range of data type

fdp_nci_create_conn() may return a negative error code, which is
silently ignored by assigning it to a u8.

Change conn_id from u8 to int to fix this.

Fixes: a06347c0 ("NFC: Add Intel Fields Peak NFC solution driver")
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>