Apply suggestions from code review

Author: vchuravy

test/devices.jl

@@ -1,14 +1,14 @@
 function devices_testsuite(Backend)
     backend = Backend()
 
-    current_device = KernelAbstractions.device!(backend)
+    current_device = KernelAbstractions.device(backend)
     for i in KernelAbstractions.ndevices(backend)
         KernelAbstractions.device!(backend, i)
         @test KernelAbstractions.device(backend) == i
     end
 
     @test_throws ArgumentError KernelAbstractions.device!(backend, 0)
     @test_throws ArgumentError KernelAbstractions.device!(backend, KernelAbstractions.ndevices(backend) + 1)
-    return KernelAbstractions.device!(backend, current_device)
     KernelAbstractions.device!(backend, current_device)
+    return nothing
 end