staging/sm75fb: Declare static functions as such

This patch fixes this sparse warning

CHECK   drivers/staging/sm750fb/ddk750_swi2c.c
drivers/staging/sm750fb/ddk750_swi2c.c:223:6: warning: symbol
  'swI2CStart' was not declared. Should it be static?
drivers/staging/sm750fb/ddk750_swi2c.c:234:6: warning: symbol
  'swI2CStop' was not declared. Should it be static?
drivers/staging/sm750fb/ddk750_swi2c.c:252:6: warning: symbol
  'swI2CWriteByte' was not declared. Should it be static?
drivers/staging/sm750fb/ddk750_swi2c.c:320:15: warning: symbol
  'swI2CReadByte' was not declared. Should it be static?
drivers/staging/sm750fb/ddk750_swi2c.c:361:6: warning: symbol
  'swI2CInit_SM750LE' was not declared. Should it be static?

Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>