i965: Convert if/else to switch statements in brw_queryobj.c

i965: Convert if/else to switch statements in brw_queryobj.c

Previously, i965 only supported two query types: GL_TIME_ELAPSED_EXT
and GL_SAMPLES_PASSED_ARB, and it distinguished between the two using
if/else statements that compared query->Base.Target to
GL_TIME_ELAPSED_EXT.

This patch changes the if/else statements to switch statements so that
we can add more query types without having to have a chain of
else-ifs.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>