staging: dwc2: add check on dwc2_core_reset return

If the GRSTCTL_CSFTRST self-clearing bit never comes
back to 0 for any reason, the controller is under reset
state and cannot be used. It's preferable to abort
initialization in such case.

Signed-off-by: Julien Delacou <julien.delacou@st.com>
Acked-by: Paul Zimmerman <paulz@synopsys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>