[arm] Fix gcc.target/arm/pr40956.c

[arm] Fix gcc.target/arm/pr40956.c

The scan-assembler tests here check for MOVS for Thumb1 and MOV for Thumb2,
but in fact there's no reason why we wouldn't generate MOVS for Thumb2 as well,
it really depends on a lot of optimisation decisions.
The only behaviour we want to test is that we move a 0 constant into a register
only once, which can be achieved with either MOV or MOVS.
Simplify the check by always checking for either MOV or MOVS.

      * gcc.target/arm/pr40956.c: Adjust scan-assembler pattern.

From-SVN: r256880