mesa: Resolve GCC missing field initializer warning.

mesa: Resolve GCC missing field initializer warning.

Resolve a series of missing field initializer warnings within get_hash_params.py

Of the form:
In file included from mesa/src/mesa/main/get.c:495:0:
mesa/src/mesa/main/get_hash.h:180:5: warning: missing initializer for field
'extra' of 'const struct value_desc' [-Wmissing-field-initializers]
     { GL_POINT_SIZE_ARRAY_BUFFER_BINDING_OES, LOC_CUSTOM, TYPE_INT, 0 },
     ^
mesa/src/mesa/main/get.c:165:15: note: 'extra' declared here
    const int *extra;
               ^

This patch addresses some likely code rot around the *extra field, where the
initialization is via C code generated indirectly from a Python script.
It resolves a number of warnings reported by GCC when configured to be pedantic.

$ gcc --version
gcc (Ubuntu 4.9.2-10ubuntu13) 4.9.2

No piglit regressions on Ironlake.

v2:
- Squash series into a single patch.

Signed-off-by: Rhys Kidd <rhyskidd@gmail.com>
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Reviewed-by: Jan Vesely <jan.vesely@rutgers.edu>
Reviewed-by: Thomas Helland <thomashelland90@gmail.com>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>