nano_init.c: STACK_CANARY_INIT fix for ARC

An updated version of ARC GCC reports this error:
nano_init.c:340: Error: inappropriate arguments for opcode 'mov'

The offending in-line assembly code tried to move register value into a
memory location.

Use store "st" instruction instead of "mov" istruction to store
a value in memory.

Change-Id: I91ebd20495612da4d5639a3ef848379705f6dedd
Signed-off-by: Juro Bystricky <juro.bystricky@intel.com>