NFC: trf7970a: Clear 'NFC Target Detection Level' register

Due to a trf7970a erratum, the 'NFC Target Detection Level' register
(0x18) must be cleared after power-up.

Signed-off-by: Mark A. Greer <mgreer@animalcreek.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

drivers/nfc/trf7970a.c

@@ -757,6 +757,11 @@ static int trf7970a_init(struct trf7970a *trf)
 	if (ret)
 		goto err_out;
 
+	/* Must clear NFC Target Detection Level reg due to erratum */
+	ret = trf7970a_write(trf, TRF7970A_NFC_TARGET_LEVEL, 0);
+	if (ret)
+		goto err_out;
+
 	ret = trf7970a_write(trf, TRF7970A_MODULATOR_SYS_CLK_CTRL,
 			TRF7970A_MODULATOR_DEPTH_OOK);
 	if (ret)