ar71xx-generic: Fix packages for GL.iNet AR750 (#1792)

The profile for GL.iNet AR750 currently selects ATH10K_PACKAGES, but this device actually has a QCA9887 which needs another driver.
This commit fixes the issue by setting ATH10K_PACKAGES_QCA9887 instead.

(cherry picked from commit 0a222183)

targets/ar71xx-generic

@@ -85,9 +85,10 @@ factory
 
 device gl.inet-gl-ar750 gl-ar750
 manifest_alias gl-ar750
-packages $ATH10K_PACKAGES
+packages $ATH10K_PACKAGES_QCA9887
 factory
 
+
 # Linksys by Cisco
 
 device linksys-wrt160nl wrt160nl WRT160NL