staging: iio: adc: add includes of module.h and stat.h

staging: iio: adc: add includes of module.h and stat.h

fixes these build problems:

drivers/staging/iio/adc/ad7746.c:345:8: error: 'S_IWUSR' undeclared here (not in a function)
drivers/staging/iio/adc/ad7746.c:436:8: error: 'S_IRUGO' undeclared here (not in a function)
drivers/staging/iio/adc/ad7746.c:681:19: error: 'THIS_MODULE' undeclared here (not in a function)
drivers/staging/iio/adc/ad7746.c:778:1: warning: data definition has no type or storage class [enabled by default]
drivers/staging/iio/adc/ad7746.c:778:1: warning: type defaults to 'int' in declaration of 'MODULE_DEVICE_TABLE' [-Wimplicit-int]
drivers/staging/iio/adc/ad7746.c:778:1: warning: parameter names (without types) in function declaration [enabled by default]
drivers/staging/iio/adc/ad7746.c:799:15: error: expected declaration specifiers or '...' before string constant
drivers/staging/iio/adc/ad7746.c:800:20: error: expected declaration specifiers or '...' before string constant
drivers/staging/iio/adc/ad7746.c:801:16: error: expected declaration specifiers or '...' before string constant

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Acked-by: Jonathan Cameron <jic23@cam.ac.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>