arch-gcn3: Fix VOP2 dissasembly prints

arch-gcn3: Fix VOP2 dissasembly prints

VOP2 prints VSRC1 register index as hex instead of decimal if the
instruction contains a literal operand.  This patch resets the
format specifiers in the stream to print the register correctly.

Change-Id: Icc7e6588b3c5af545be6590ce412460e72df253f
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/29936
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Anthony Gutierrez <anthony.gutierrez@amd.com>
Maintainer: Anthony Gutierrez <anthony.gutierrez@amd.com>