remoteproc: ti_k3_m4_remoteproc: Fix unused-but-set-variable warnings

Drop following unused variables

All warnings (new ones prefixed by >>):

   drivers/remoteproc/ti_k3_m4_remoteproc.c: In function 'k3_m4_rproc_start':
   drivers/remoteproc/ti_k3_m4_remoteproc.c:333:13: warning: variable 'boot_addr' set but not used [-Wunused-but-set-variable]
     333 |         u32 boot_addr;
         |             ^~~~~~~~~
   drivers/remoteproc/ti_k3_m4_remoteproc.c: In function 'k3_m4_rproc_resume':
   drivers/remoteproc/ti_k3_m4_remoteproc.c:916:13: warning: variable 'ret' set but not used [-Wunused-but-set-variable]
     916 |         int ret = 0;
         |             ^~~

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>