NFC: trf7970a: Disable SYS_CLK Output

Currently, support for providing the external
SYS_CLK signal on pin 27 is not supported so
turn it off by writing to the 'Modulator and
SYS_CLK Control' register immediately after
reset.
Signed-off-by: Mark A. Greer <mgreer@animalcreek.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

drivers/nfc/trf7970a.c

@@ -775,6 +775,12 @@ static int trf7970a_init(struct trf7970a *trf)
 	if (ret)
 		goto err_out;
 
+	ret = trf7970a_write(trf, TRF7970A_MODULATOR_SYS_CLK_CTRL, 0);
+	if (ret)
+		goto err_out;
+
+	trf->modulator_sys_clk_ctrl = 0;
+
 	/* Must clear NFC Target Detection Level reg due to erratum */
 	ret = trf7970a_write(trf, TRF7970A_NFC_TARGET_LEVEL, 0);
 	if (ret)