gpio: stmpe: fix interrupt handling bug

gpio: stmpe: fix interrupt handling bug

commit 01b1a98a6e5e ("gpio: stmpe: Rework registers access")
reworked the STMPE register access so as to use
[STMPE_IDX_*_LSB + i] to access the 8bit register for a
certain bank, assuming the CSB and MSB will follow after
the enumerator. For this to work the index needs to go from
(size-1) to 0 not 0 to (size-1).

However for the GPIO IRQ handler, the status registers we read
register MSB + 3 bytes ahead for the 24 bit GPIOs and index
registers from MSB upwards and run an index i over the
registers UNLESS we are STMPE1600.

This is not working when we get to clearing the interrupt
EDGE status register STMPE_IDX_GPEDR_[LCM]SB: it is indexed
like all other registers [STMPE_IDX_*_LSB + i] but in this
loop we index from 0 to get the right bank index for the
calculations, and we need to just add i to the MSB.

Before this, interrupts on the STMPE2401 were broken, this
patch fixes it so it works again.

Cc: stable@vger.kernel.org
Cc: Patrice Chotard <patrice.chotard@st.com>
Fixes: 01b1a98a6e5e ("gpio: stmpe: Rework registers access")
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>