ACPI / SBS: Fix check in acpi_ac_get_present()

Parentheses are missing under an if () statement in
acpi_ac_get_present() which makes the check work differently
from what was intended (at least according to the comment right
above it).  Add the missing parens.

The problem was found by sparse.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: All applicable <stable@vger.kernel.org>

drivers/acpi/sbs.c

@@ -441,7 +441,7 @@ static int acpi_ac_get_present(struct acpi_sbs *sbs)
 	 * The spec requires that bit 4 always be 1. If it's not set, assume
 	 * that the implementation doesn't support an SBS charger
 	 */
-	if (!(status >> 4) & 0x1)
+	if (!((status >> 4) & 0x1))
 		return -ENODEV;
 
 	sbs->charger_present = (status >> 15) & 0x1;