mesa: Remove gratuitous padding in prog_dst_register.

The padding was there to indicate the amount of space left from the
number of expected bytes in the struct minus allocated bits.  But
uint bitfields get packed so that they don't cross uint boundaries, and we
ended up allocating an extra dword to hold the pad field!

src/mesa/drivers/dri/i965/brw_wm_fp.c

@@ -138,7 +138,6 @@ static struct prog_dst_register dst_reg(GLuint file, GLuint idx)
    reg.CondMask = COND_TR;
    reg.CondSwizzle = 0;
    reg.CondSrc = 0;
-   reg.pad = 0;
    return reg;
 }
 

src/mesa/main/ffvertex_prog.c

@@ -523,7 +523,6 @@ static void emit_dst( struct prog_dst_register *dst,
    dst->CondMask = COND_TR;  /* always pass cond test */
    dst->CondSwizzle = SWIZZLE_NOOP;
    dst->CondSrc = 0;
-   dst->pad = 0;
    /* Check that bitfield sizes aren't exceeded */
    ASSERT(dst->Index == reg.idx);
 }

src/mesa/shader/prog_instruction.h

@@ -312,7 +312,6 @@ struct prog_dst_register
     */
    GLuint CondSrc:1;
    /*@}*/
-   GLuint pad:28;
 };