prog_to_nir: Make RSQ properly take the absolute value of its argument.

prog_to_nir: Make RSQ properly take the absolute value of its argument.

I just botched this when writing the original code.

From the ARB_vertex_program specification:
"The RSQ instruction approximates the reciprocal of the square root of
 the absolute value of the scalar operand and replicates it to all four
 components of the result vector."

Fixes a Glean vertProg1 subtest:
RSQ test 2 (reciprocal square root of negative value)

Cc: mesa-stable@lists.freedesktop.org
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=90547
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Francisco Jerez <currojerez@riseup.net>