Staging: iio: Use braces on all arms of if statement

Add braces to improve consistency when using if statements.
Found by checkpatch.pl:
"CHECK: braces {} should be used on all arms of this statement".

Signed-off-by: Cristina Opriceana <cristina.opriceana@gmail.com>
Reviewed-by: Daniel Baluta <daniel.baluta@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>