[ARM] Fix nwbutton sparse warnings

[ARM] Fix nwbutton sparse warnings

drivers/char/nwbutton.c:177:24: warning: incorrect type in argument 1 (different address spaces)/home/rmk/bk/linux-2.6-rmk/drivers/char/nwbutton.c:177:24:    expected void [noderef] *to<asn:1>
drivers/char/nwbutton.c:177:24:    got char *buffer
drivers/char/nwbutton.c:177:24: warning: incorrect type in initializer (different address spaces)
drivers/char/nwbutton.c:177:24:    expected void [noderef] *to<asn:1>
drivers/char/nwbutton.c:177:24:    got char *buffer
drivers/char/nwbutton.c:189:11: warning: incorrect type in initializer (incompatible argument 2 (different address spaces))
drivers/char/nwbutton.c:189:11:    expected int [usertype] ( *read )( ... )
drivers/char/nwbutton.c:189:11:    got int ( static [addressable] [toplevel] *<noident> )( ... )