drivers/staging/greybus: gpio.c - Fixed a checkpatch generated warning

Removed braces for single line if statement.

Signed-off-by: Chase Metzger <chasemetzger15@gmail.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>