[Sparc][Leon] Corrected supported atomics size for processors supporting Leon...

[Sparc][Leon] Corrected supported atomics size for processors supporting Leon CASA instruction back to 32 bits.

This was erroneously checked-in for 64 bits while trying to find if there was a way to get 64 bit atomicity in Leon processors. There is not and this change should not have been checked-in. There is no unit test for this as the existing unit tests test for behaviour to 32 bits, which was the original intention of the code.

llvm-svn: 280710