mfd: stmpe: Fix RESET regression on STMPE2401

Since commit c4dd1ba355
("mfd: stmpe: Add reset support for all STMPE variant")
we're resetting the STMPE expanders before use.

This caused a regression on the STMP2401 on the Nomadik
NHK8815:

stmpe-i2c 0-0043: stmpe2401 detected, chip id: 0x101
nmk-i2c 101f8000.i2c0: write to slave 0x43 timed out
nmk-i2c 101f8000.i2c0: no ack received after address transmission
stmpe-i2c 0-0044: stmpe2401 detected, chip id: 0x101
nmk-i2c 101f8000.i2c0: write to slave 0x44 timed out
nmk-i2c 101f8000.i2c0: no ack received after address transmission

It turns out that we start to poll for the reset bit to
go low again too quickly: the STMPE2401 is not yet online and
ready to be asked for the status of the RESET bit.

By introducing a 10ms delay before starting to hammer
the register for information, we get back to normal:

stmpe-i2c 0-0043: stmpe2401 detected, chip id: 0x101
stmpe-i2c 0-0044: stmpe2401 detected, chip id: 0x101

Cc: stable@vger.kernel.org
Cc: Amelie Delaunay <amelie.delaunay@st.com>
Fixes: c4dd1ba355 ("mfd: stmpe: Add reset support for all STMPE variant")
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Patrice Chotard <patrice.chotard@st.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/mfd/stmpe.c

@@ -851,6 +851,8 @@ static int stmpe_reset(struct stmpe *stmpe)
 	if (ret < 0)
 		return ret;
 
+	msleep(10);
+
 	timeout = jiffies + msecs_to_jiffies(100);
 	while (time_before(jiffies, timeout)) {
 		ret = __stmpe_reg_read(stmpe, stmpe->regs[STMPE_IDX_SYS_CTRL]);