Add __iomem to the apbps2_priv.regs field to make the numerous
warnings about differing address spaces go away. Fixes warnings
such as:

drivers/input/serio/apbps2.c:65:26: warning: incorrect type in argument 1 (different address spaces)
drivers/input/serio/apbps2.c:65:26:    expected void const volatile [noderef] <asn:2> *addr
drivers/input/serio/apbps2.c:65:26:    got unsigned int [noderef] *
drivers/input/serio/apbps2.c:65:26: warning: incorrect type in argument 1 (different address spaces)
drivers/input/serio/apbps2.c:65:26:    expected void const volatile [noderef] <asn:2> *addr
drivers/input/serio/apbps2.c:65:26:    got unsigned int [noderef] *
drivers/input/serio/apbps2.c:65:26: warning: incorrect type in argument 1 (different address spaces)
drivers/input/serio/apbps2.c:65:26:    expected void const volatile [noderef] <asn:2> *addr
drivers/input/serio/apbps2.c:65:26:    got unsigned int [noderef] *
drivers/input/serio/apbps2.c:65:26: warning: incorrect type in argument 1 (different address spaces)
drivers/input/serio/apbps2.c:65:26:    expected void const volatile [noderef] <asn:2> *addr
[rest snipped]
Signed-off-by: Ben Dooks (Codethink) <ben.dooks@codethink.co.uk>
Link: https://lore.kernel.org/r/20191217122507.2157454-1-ben.dooks@codethink.co.ukSigned-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>