media: platform: return early if the iface is not handled

Clang static analysis reports this issue
ispcsiphy.c:63:14: warning: The left operand of '<<'
  is a garbage value
        reg |= mode << shift;
               ~~~~ ^
The iface switch-statement default case falls through
to ISP_INTERFACE_CCP2B_PHY1.  Which is later checked
to set the mode.  Since the default case is left out
of this check mode is never set.  Instead of falling
through and assuming a ISP_INTERFACE_CCP2B_PHY1
iface, return.

Signed-off-by: Tom Rix <trix@redhat.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>