bus: mhi: core: Fix shadow declarations

bus: mhi: core: Fix shadow declarations

This commit fixes below sparse warnings with W=2 about shadow
declarations:

drivers/bus/mhi/core/main.c: In function ‘parse_xfer_event’:
drivers/bus/mhi/core/main.c:667:17: warning: declaration of ‘flags’ shadows a previous local [-Wshadow]
  667 |   unsigned long flags;
      |                 ^~~~~
drivers/bus/mhi/core/main.c:565:16: note: shadowed declaration is here
  565 |  unsigned long flags = 0;
      |                ^~~~~
drivers/bus/mhi/core/main.c: In function ‘mhi_process_ctrl_ev_ring’:
drivers/bus/mhi/core/main.c:856:23: warning: declaration of ‘new_state’ shadows a previous local [-Wshadow]
  856 |     enum mhi_pm_state new_state;
      |                       ^~~~~~~~~
drivers/bus/mhi/core/main.c:837:19: note: shadowed declaration is here
  837 |    enum mhi_state new_state;
      |                   ^~~~~~~~~

Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>