Staging: mrst-touchscreen - simplify en/disable of interrupts for NEC

Use 8 bit update commands instead of a 16 bit unaligned read/write
pair which fails after the first few calls; the voodoo in the original
doesn't seem to be required with this mechanism.

Tested-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Andy Ross <andy.ross@windriver.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>