USB: OTG: msm: Fix error handling in probe

If clk_get on core_clk fails in probe function, the return value
is incorrectly assigned.  Assign the ret variable to the error
code returned for core_clk not alt_core_clk.

Change-Id: Icca82e8e44cd40149205c246f427ab82e4656268
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>