i965/fs: Set stride correctly for immediates in fs_reg(brw_reg).

i965/fs: Set stride correctly for immediates in fs_reg(brw_reg).

The fs_reg() constructors for immediates set stride to 0, except for
vector-immediates, which set stride to 1.  This patch makes the fs_reg
constructor that takes a brw_reg do likewise, so that stride is set
correctly for cases such as fs_reg(brw_imm_v(...)).

The generator asserts that this is true (and presumably it's useful in
some optimization passes?) and the VF fs_reg constructors did this (by
virtue of the fact that it doesn't override what init() does).

In the next commit, calling this constructor with brw_imm_* will generate
an IMM file register rather than a HW_REG, making this change necessary
to avoid breakage with existing uses of brw_imm_v().

Reviewed-by: Emil Velikov <emil.velikov@collabora.co.uk>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>