i965: Fix src0 vs src1 typo

i965: Fix src0 vs src1 typo

A typo caused us to copy src0's reg file to src1 rather than reading
src1's as intended. This caused us to fail to compact instructions like

   mov(8)   g4<1>D    0D              { align1 1Q };

because src1 was set to immediate rather than architecture file. Fixing
this reenables compaction (after the precompact() pass changes the data
types):

   mov(8)   g4<1>UD   0x00000000UD    { align1 1Q compacted };

Fixes: 1cb0a7941b27 ("i965: Switch to using the logical register types")
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>