glsl: Always strip arrayness in precision_qualifier_allowed

glsl: Always strip arrayness in precision_qualifier_allowed

Previously some callers of precision_qualifier_allowed would strip the
arrayness from the type and some would not.  As a result, some places
would not notice that float[6], for example, needed a precision
qualifier.

Fixes the new piglit test no-default-float-array-precision.frag.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=96358
Cc: "12.0" <mesa-stable@lists.freedesktop.org>
Cc: Gregory Hainaut <gregory.hainaut@gmail.com>
Cc: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Timothy Arceri <timothy.arceri@collabora.com>