platform/x86: acer-wmi: refactor function has_cap

Refactor function has_cap in order to avoid returning integer
values, when instead it should return booleans.

This code was detected with the help of Coccinelle.

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Reviewed-by: "Lee, Chun-Yi" <jlee@suse.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>