msm: kgsl: fix a condition error and set L3 clock rate fail

Fix a condition error in gmu_enable_clks, if there is no hub_clk
exists, the return value should be -ENODEV.
There will be an set L3 clock failure while kgsl power disable,
we should set L3 clock to NULL while there is no l3_vote clock
exists:
[   13.076919] Call trace:
[   13.079430]  clk_set_rate+0x78/0x140
[   13.083103]  kgsl_pwrctrl_disable+0x20/0x270
[   13.087491]  _slumber+0x24c/0x280
[   13.090893]  kgsl_pwrctrl_change_state+0x384/0x640

Change-Id: I492ce86908ade3daba526f8c3d269ba05c07e2aa
Signed-off-by: Hui Li <hul@codeaurora.org>