ldlinux: Fix compiler warnings in cli.c

ldlinux: Fix compiler warnings in cli.c

Make the compiler happy by casting away the following warnings,

cli.c: In function ‘process_command’:
cli.c:381:2: warning: passing argument 1 of ‘strtok’ discards qualifiers from pointer target type
../../../com32/include/string.h:44:16: note: expected ‘char *’ but argument is of type ‘const char *’
cli.c:400:3: warning: passing argument 2 of ‘spawn_load’ from incompatible pointer type
../../../com32/include/sys/exec.h:43:12: note: expected ‘const char **’ but argument is of type ‘char **’

Signed-off-by: Matt Fleming <matt.fleming@linux.intel.com>