intel: Silence many "intel_batchbuffer.h:97:39: warning: comparison between signed...

intel: Silence many "intel_batchbuffer.h:97:39: warning: comparison between signed and unsigned integer expressions"

v2: Remove the assertion in intel_batchbuffer_space:

   assert((intel->batch.state_batch_offset - intel->batch.reserved_space)
	  >= intel->batch.used*4);

After reviewing all the places where this is called, I'm (fairly)
comfortable that this assertion was redundant.  Having the assertion
adds ~20KiB to a driver build:

   text	   data	    bss	    dec	    hex	filename
 903173	  26392	   1552	 931117	  e352d	i965_dri.so
 924093	  26392	   1552	 952037	  e86e5	i965_dri.so

Based on feedback from Eric Anholt.

Reviewed-by: Eric Anholt <eric@anholt.net>