MIPS/testsuite: Fix umips-save-restore-1.c

With some recent optimization, -O1/-O2/-O3 can archive almost same
performace/size by stack load/store.  Thus lwm/swm will save/store
less callee-saved register.  In fact only $16 is saved with swm.

To be sure that this optimization does exist, let's add 2 more
function calls.  So that lwm/swm can be much more profitable.

If we add only once more, -O1 will still use stack load/store.

gcc/testsuite
	* gcc.target/mips/umips-save-restore-1.c: Be sure lwm/swm
	are used for more callee-saved registers with addtional
	2 more function calls.