cpu: Fix vector renaming bug

cpu: Fix vector renaming bug

The following patch:

https://gem5-review.googlesource.com/c/public/gem5/+/25009

moved initialization of vecMode out of initializing list.
In this way regFile gets initialized with an invalid initial renaming
mode.

Change-Id: Ib7bab9eaac0f5850fd3b3151584132f809a641e1
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/25430
Reviewed-by: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>