MIPS/GAS/testsuite: Fix `-modd-spreg'/`-mno-odd-spreg' test invocations

Reformat `-modd-spreg'/`-mno-odd-spreg' test invocations in mips.exp to
fit in 79 columns

	gas/
	* testsuite/gas/mips/mips.exp: Reformat
	`-modd-spreg'/`-mno-odd-spreg' test invocations.