phy-msm-usb : Do clk_get for optional alt_core_clk after mandatory clk

Linux clock driver API implementation for clk_get() has changed where
it returns -EPROBE_DEFER when clock is not found. As "alt_core_clk"
is optional for msm_otg and calling clk_get() for "alt_core_clk"
is returning -EPROBE_DEFER, msm_otg_probe keeps on retrying and never
succeds.

Fixing the issue by doing clk_get() for optional "alt_core_clk" after
all mandatory clocks. If all the mandatory clock gets succeed, then
failure of the optional clock means the clock is not there and hence
do not reurn -EPROBE_DEFER for optional clock from msm_otg_probe.

CRs-Fixed: 590336
Change-Id: Ib9e9d509858b32a1e2933fee1c1233cf13e007e4
Signed-off-by: Saket Saurabh <ssaurabh@codeaurora.org>