input: synaptics_i2c_rmi4: allocate memory for interrupt status

In synaptics_rmi4_i2c_read, intr_status is a char variant.  So
if num_of_intr_regs > 1, then intr_status will write 2 bytes.  This
will destroy the stack, so avoid it.

Change-Id: I5c16e491a84d3f8dd96a11810c060944a457b99a
Signed-off-by: Amy Maloche <amaloche@codeaurora.org>